The penile volume responses of homosexual males to pictures of nude women and men were measured and related to the subjects' marital status and experience of heterosexual intercourse. Single subjects with no experience of heterosexual intercourse and married subjects with a history of intercourse with only their wives showed significantly greater response to pictures of men compared to pictures of women than did single subjects with experience of heterosexual intercourse and married subjects with experience of intercourse with women additional to their wives. It was concluded that extensive experience of heterosexual intercourse with one partner did not reduce homosexual responsiveness as measured by subjects' penile response to pictures of nude men and women. It was further concluded that some homosexual males showed physiological evidence of a degree of bisexuality in addition to the behavioral evidence that they sought heterosexual physical relationships.