When Leonard Bernstein commissioned Kay to orchestrate his musical comedy On the Town in 1944, Kay became one of the most sought after orchestrators on Broadway. Later collaborations with Bernstein include Peter Pan (1950) and Candide (1956). Kay also did orchestrations for Marc Blitzstein (Juno), Harvey Schmidt (110 in the Shade), Cy Coleman (Barnum) and Andrew Lloyd Webber (Evita). In 1954, George Balanchine commissioned Kay to compose the score for his ballet Western Symphony, set in the American West. Kay later wrote the score for Balanchine’s Stars and Stripes based on John Philip Sousa’s music.
A composer in his own right, Hershy Kay’s reconstruction and
orchestration of Louis Moreau Gottschalk’s Grande Tarantelle,
Op. 67, for piano and orchestra July 24, 1957, later choreographed by
Balanchine as Tarantella, led to a renewed interest in Gottschalk’s
music. He also composed music for an LP, Mother Goose, with
the actors Boris Karloff, Cyril Ritchard and Celeste Holm; this was
first released on Caedmon in 1958. He also orchestrated Sigmund Romberg's
music in a 1963 Columbia Masterworks recording of selections from the
1924 operetta The Student Prince, starring Roberta Peters, Jan Peerce,
and Giorgio Tozzi.