Roger Corman actually used several members of the real Hell's Angels as extras.
George Chakiris was originally hired by Roger Corman to play "Black Jack" (later changed to "Heavenly Blues" by Peter Fonda), but insisted that a stunt double do his motorcycle riding, so Corman replaced him with Fonda, who was originally cast as "Loser".
Actress Laura Dern (daughter of Bruce Dern and Diane Ladd) was conceived during the movie shoot. Growing up, she sometimes showed people who asked about her parents a still of them in their biker outfits.
Around the time of shooting the funeral for 'Loser' outside of the church at North Argyle, Bruce Dern was assaulted and beaten by two real Hell's Angels; Dern tried to explain he was in a movie, but the bikers didn't believe him and knocked him out cold on the sidewalk. Later, Bruce said: "It was, like, hey, I'm not even alive in the movie, I'm dead, and they're STILL beating on me..."
The film was initially refused a UK cinema certificate in 1966 and eventually passed with cuts in 1972. Later video and DVD releases were fully uncut.
The Hells Angels brought a $5-million defamation lawsuit against Roger Corman for what they perceived as a negative portrayal of their image.
The quote "we wanna get loaded...." was used by Primal Scream as the intro to their song "Loaded", which was first released in 1991 on the album "Screamadelica".