Selected sexual practices of San Francisco heterosexual men and risk of infection by the human immunodeficiency virus.
D000163:Acquired Immunodeficiency Syndrome / Q000453:epidemiology*; D000328:Adult; D002140:California; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012306:Risk; D012725:Sexual Behavior