After November 1956, the study of new scores and singing on stage became very frequent. In 1957, the debut in Falstaff, in 1958 as Alfredo in Traviata co-starring the great Greek soprano Maria Callas for the only time ever. Callas, as Kraus recalled, was a terrific woman and colleague. She showed an incredible kindness and insisted that he be with her to receive enthusiastic accolades at the end of Act II. In 1958, the debut in Don Pasquale with Renata Scotto, in the Pearl Fishers with Gino Bechi and in Marina, a zarzuela of Pascual Juan Emilio Arrieta y Correra. Kraus thought highly of zarzuelas, which he kept singing during recitals. At the end of a triumphant concert in Florence with a program entirely dedicated to music of his land, Kraus remarked: ”Zarzuelas are music little known in the world and unjustly so.” In 1960, as Pinkerton in Madama Butterfly and Verdi’s Requiem for the only time, in 1961 debut in Puritani, in 1962 in Favorita and the United States. Debut in Elisir d’amore at the Met in late 1962, L’heure espagnole of Ravel and Carmina Burana of Orff at Chicago in late 1965.

1965 was a significant year in the career and life of the great Spaniard. Kraus made his debut as the poet in the principal role of Werther, with Anna Maria Rota as Carlotta and Franco Bordoni as Alberto. The venue was the Teatro Municipale di Piacenza, Italy. In a memorable night, he encored the aria of Act III, “Pourquoi me reveiller”. Kraus showed an extraordinary vocal and scenic affinity with the tragic hero of Massenet. In the ensuing years, his role interpretation of Werther was complete, reaching a perfect union of elegiac intimacy and passionate ardour, destined to enter history and gain him fame all over the world, following Tito Schipa’s example. However, Kraus confessed that, as a modern tenor, he identified himself better in the role of Traviata’s Alfredo and equally in those of Arturo, Edgardo, Fernando, Hoffman, Nemorino and Tonio (Figlia del reggimento).

In the summer of 1968, Kraus was at Salzburg, invited to sing in Don Giovanni by no other than the very famous orchestra conductor, Herbert von Karajan. For Don Giovanni, Karajan had assembled a stunning cast: Nicolaj Ghiaurov in the principal role, Gundula Janowitz, Teresa Zylis-Gara, Mirella Freni, Geraint Evans, Rolando Panerai, Martti Talvela and Alfredo Kraus. The tenor’s collaboration with the Austrian conductor was interesting because they shared the conviction that role characterization in all Mozart operas lies in the recitatives. Kraus said: “They should be executed “all’italiana”, with the correct expression so that audiences may understand what goes on the stage. This belief is in contrast with that of many conductors, Mozart music celebrated readers, who frequently forget that also the recitatives exist”. Kraus became worried when Karajan asked him to exercise nothing but recitatives for three weeks. After querying him, Karajan replied: ”Do not worry about arias. I know how you sing." Kraus returned to Salzburg the following year, but refused to participate at the Festival for the summer of 1970. He explained to Karajan that he had already made two exceptions to be at Salzburg in summer, depriving his family of their vacation season. Karajan understood and paid him an open tribute of esteem: “Be aware that I have great respect for you and your art.” They parted very cordially as usual. They never worked together again.

The seventies and eighties coincided with a larger repertory embracing new operas by Donizetti such as Linda di Chamounix, La figlia del reggimento, Lucrezia Borgia and French opera such as Contes d’Hoffmann, Romeo et Juliette, Lakmé as well as an intensification of old roles such as Werther, Des Grieux, Nadir and Faust. Kraus’ popularity in Italy increased considerably with the marketing of a series of records of the early sixties in the wake of a biographical film on Julian Gayarre, the great Spanish tenor, with a rich sound track of operatic highlights and Spanish songs. It is worth a mention here that José Carreras also portrayed Julian Gayarre in another film entitled Romanza Final. Many zarzuela selections and a full opera, The Pearl Fishers, featured in long playing operatic records, later marketed by a record company, Carillon Records, and distributed in Italy by the House of Giancarlo Bongiovanni.