IN mammals, including man, specific sexual stimuli can affect the secretion of luteinising hormone (LH) from the pituitary and testosterone from the testis. For example, the presence of the female and copulation is associated with an increase in the blood levels of testosterone in rabbit1, rat2, bull3 and man4, and in each species excluding man this has been shown to be related to an elevation of blood plasma LH1,3,5. Among animals, merely the presence of a receptive female may induce these changes in the absence of intercourse2,3,5 indicating that in some species visual and olfactory cues alone are sufficient to elicit an endocrine response. In man the anticipation of female company after long periods of abstinence apparently has similar effects6. Very few studies of this sort have looked at both LH and testosterone secretion simultaneously in sufficient detail to provide convincing evidence of short term endocrine changes related to behaviour. The aim of my study was to establish whether the normal pulsatile secretion of LH and testosterone in men could be altered by a specific sexual stimulus. It was decided to expose male volunteers to a film sequence which included scenes of human behaviour which were judged to be sexually provocative.