The band Earth, Wind & Fire's fictional name is The Group, but there's an Earth, Wind & Fire billboard in one scene (shown prominently, as if deliberate).
Murray Mosten plays the father of Harvey Keitel's character. Mosten and Keitel were frequently cast by Martin Scorsese, and many times in the same films, before and after this movie (including Taxi Driver).
Jimmy Boyd, who plays the drug addict singer of The Page group (who are supposed to have a straight-laced image), was the singer of the famous song "I Saw Mommy Kissing Santa Claus" at thirteen years old.