Greenfield worked as a messenger for National Cash Register. In 1958, Greenfield and Sedaka signed to Al Nevins and Don Kirshner's Aldon Music as songwriters, which had offices at 1650 Broadway in New York. (The company later moved to the Brill Building.) In their first year there, Greenfield and Sedaka wrote material for Jimmy Clanton and Bobby Darin, and scored their first major pop hit single with Connie Francis' "Stupid Cupid", which hit #14 on the US pop charts in September 1958. They also wrote Francis' later hits, "Fallin'", "Frankie", and the "Theme to Where the Boys Are," the film in which she starred. When, in 1958, Sedaka signed to RCA Records as a solo artist, he and Greenfield composed a string of hits for Sedaka to record – among them "The Diary", "Oh! Carol", "Stairway to Heaven", "Calendar Girl", "Little Devil", "Happy Birthday Sweet Sixteen", "Next Door to an Angel" and the chart-topping "Breaking Up Is Hard to Do". Sedaka's recordings eventually sold a combined 25 million records. As Sedaka's promotional and touring commitments began taking up more and more of his time, Kirshner encouraged Greenfield to collaborate with other Aldon writers. Beginning in 1960, Greenfield began a regular collaboration with Jack Keller; they would write songs together every Monday and Wednesday for six straight years. Successful Greenfield/Keller collaborations included two consecutive US #1 hits for Connie Francis, "Everybody's Somebody's Fool" and "My Heart Has a Mind of Its Own". They wrote another Francis top 10 hit, "Breakin' in a Brand New Broken Heart", Jimmy Clanton's top 10 hit "Venus in Blue Jeans", as well as songs recorded by Frank Sinatra, Ernest Tubb, Patti Page and Brenda Lee. Greenfield and Keller also supplied the theme music for U.S. television programs such as Gidget and Bewitched. Greenfield also collaborated with other Aldon songwriters, including Helen Miller, with whom he co-wrote "Foolish Little Girl" (the Shirelles' final Top Ten hit), "It Hurts to Be in Love", originally intended for Neil Sedaka but ultimately recorded by Gene Pitney, as well as a new theme for the TV series Hazel for its fourth season. He also collaborated with Bill Buchanan recording a novelty record called "The Invasion" as Buchanan and Greenfield in 1964. As well, Greenfield's one and only collaboration with Aldon songwriter Carole King resulted in "Crying in the Rain", a top ten hit for the Everly Brothers in 1962. The collaboration