Regardless of the self-doubts now plaguing Lanza, to his colleagues there was never any question of his ability to perform on the stage. As soprano Dorothy Kirsten, who worked with Lanza on The Great Caruso, reminisced years later, "He could have sung in any opera house in the world, and his career could have been sensational." George London concurred:

In my opinion, Lanza, with the possible exception of Bjoerling, had the greatest voice of his time. His singing could move people to tears and, in my presence, frequently did. His Hollywood experience undermined his inner security, which is why he avoided performing in public. I would venture that if he had not gone to Hollywood he would, at least for the beginning, have had a major operatic career.

Such was Lanza's insecurity by now that he did not sing again on the concert stage for six and a half years after his record-breaking tour of 1951. In the interim his film career unravelled, and with it his lifestyle. Louis B. Mayer had been replaced at MGM by Dore Schary, a man with whom Lanza repeatedly clashed over his demands for greater artistic standards in his films. Dismissed by MGM in 1952 after he had pre-recorded the songs for The Student Prince, Lanza also endured the double blow of near-bankruptcy arising from a number of bad investments made by his former manager. Pursued by the IRS for $250,000 in back taxes – and his film career now in tatters – Lanza increasingly sought refuge in alcohol. In no position, either emotionally or physically, to contemplate a return to live performing, for the next two years Lanza remained a virtual recluse.

The years of inactivity ended with his return to films in Serenade (1956) for Warner Bros. His voice by now considerably rounder and darker, but retaining its thrilling upper register, Lanza worked diligently with vocal coach Giacomo Spadoni on the operatic numbers for the movie. Perhaps inevitably – given his long period of inactivity – some of the singing was uneven, but overall Serenade represented a formidable achievement. On the best numbers, Lanza's singing was more controlled and operatic than it had been in his MGM days. The highlights included superb renditions of the arias Amor Ti Vieta, Di Rigori Armato, and the Otello Monologue, and the Neapolitan song Torna a Surriento. The Otello Monologue is arguably Lanza's finest operatic recording, and offers compelling evidence of the intelligence and conviction that the tenor could have brought to the role on stage.

Lanza also recorded the Act III duet Dio Ti Giocondi from Otello with the Metropolitan soprano Licia Albanese. Over 20 years later Albanese recalled their collaboration:

I had heard all sorts of stories about Mario. That his voice was too small for the stage, that he couldn't even sing a full aria [...] None of it is true! He had the most beautiful lirico spinto voice. It was a gorgeous, beautiful, powerful voice. I should know because I sang with so many tenors. He had everything that one needs. The voice, the temperament, perfect diction. He also had an infallible instinct for what was good for his voice and knew exactly how to move on a stage. [...] Vocally, he was very secure. All he needed was coaching. Everything was so easy for him. He was fantastic! I rank him next to Caruso. Next comes Di Stefano, then all the others.

Renata Tebaldi visited Lanza on the set of Serenade in December 1955, and later attended a screening of the musical highlights from the film. "Tebaldi was so overcome by Mario's singing that she was moved to tears," recalled the film's musical director Ray Heindorf. She also spent an evening at Lanza's home, where the two singers sang together. Her response to hearing his live voice was unequivocal. "Yours is the finest natural tenor voice I have ever heard," she told Lanza.

Mario Lanza preparing to sing Otello in Serenade (1956). Photo courtesy of Armando Cesari.

However, Serenade's strong musical content did not help it at the box office, where it was the least successful of the tenor's five films to date. Its failure helped to convince Lanza that it was time to seek a fresh start in Europe. Moving with his family to Rome, Italy in May 1957, Lanza immediately began work on a new film entitled The Seven Hills of Rome. Indisputably his weakest cinematic effort, both dramatically and musically, Seven Hills was nevertheless a commercial success, particularly in Italy, where it was the fourth most popular release of 1958.

More importantly, Lanza's move to Europe signalled a return to live performing. Beginning with an acclaimed Command Performance at the London Palladium in November 1957, Lanza received excellent reviews for his singing. His sold-out tour of Britain and the Continent in 1958 included a recital at the Royal Albert Hall in the presence of such operatic luminaries as Nicolai Gedda, Joan Sutherland, and Richard Bonynge. Although Lanza was in thrilling voice, stylistically his singing on this occasion left much to be desired. Nevertheless, Gedda would state that, "It's the greatest tenor voice I've ever heard." Years later Bonynge recalled the occasion:

We were both surprised by the size of the voice. After all, one hears how film singers' voices are amplified. We were also impressed by Lanza's innate musicality. No doubt he could have had an outstanding operatic career.

However, the tour also signalled the beginning of the tenor's physical decline. Afflicted with a debilitating attack of phlebitis in his right leg, and suffering from extremely high blood pressure – largely the result of years of heavy drinking and crash dieting – Lanza's health was rapidly deteriorating. Although warned of the possibility of pulmonary embolism arising from the phlebitis, Lanza ignored his doctor's concerns and resumed his concert tour. He also announced that he would make yet another film.

The movie, ironically entitled For the First Time, revealed that in spite of his ailments, Lanza had not only matured as an artist, but that he was in the best vocal form of his life. Under the guidance of coaches Annibale Bizzelli and Franco Zauli, the tenor gave impressive renditions of a number of operatic selections, including the arias Vesti la Giubba from Pagliacci and Niun Mi Tema from Otello. Recorded at the Rome Opera House in August 1958, both performances are devoid of the mannerisms that had sometimes marred his earlier operatic work. Skillfully modulating his dark, baritonal colouring on these arias to suit the lyric requirements of Mozart, Lanza also sings the sparkling trio E Voi Ridete from Così Fan Tutte with two soloists from the Rome Opera.

Present at the recording sessions was Riccardo Vitale, Artistic Director of the Rome Opera. Impressed by what he later described as Lanza's "exceptional timbre and great musicality," Vitale invited the tenor to open a season there in any opera of his choosing. As news of Vitale's offer spread, identical invitations were made by the management of La Scala and San Carlo. Lanza eventually accepted Vitale's offer, agreeing to open the 1960/61 Rome Opera season as Canio in Pagliacci.

A number of other operatic projects were also announced, including a 90-minute television spectacular with Maria Callas, and a series of complete opera recordings for RCA in Bologna.

But it was all too late. Lanza's health was already irreversibly in decline, and he had only a year to live. He was now suffering from liver damage, gout, arteriosclerosis, and the ever-present phlebitis. A minor heart attack in April 1959, followed by a bout of double pneumonia in August, hastened the decline, and on October 7th 1959 he died in Rome of a pulmonary embolism at the age of 38. His grief-stricken widow would outlive him by just five months.