 Prior to leaving Jamaica he worked on recordings by various foreign acts who gravitated to Jamaica's studios, including Paul Simon, Eddie Kendricks, Peter Paul & Mary, and Booker T. and the MGs.Just before leaving Jamaica he also appeared in the classic film "The Harder They Come", as well as playing on most of the soundtrack cuts.In 1973 Grennan relocated to America "to study jazz" where he embarked on sessions with saxophonist Robin Kenyatta.