To determine whether changes in LH and testosterone (T) blood levels and pulse signals were induced by sexual arousal, nine healthy young males were presented on two different days with a sexually arousing (S) and a sexually neutral control (C) film. On both sessions, blood was sampled every 10 min for 12 hr. The Cluster and the Detect pulse identification algorithms were used to characterize the peaks in LH and T series. The second plasma LH peak following the beginning of the film was higher in the S than in the C condition (percent increases above preceding nadir: 322.1 +/- 183.9% vs. 202.6 +/- 108.7%). The area of the second pituitary peak of LH instantaneous secretion rate, which corresponded to the second plasma LH peak, was also greater in the S condition (6.2 +/- 3.3 vs. 3.4 +/- 2.3 UI/l). Compared with the C condition, T blood levels were increased within the first 10 min of sexual arousal (25.2 +/- 6.3 vs. 22.2 +/- 5.6 nmol/l). These results, consistent with the findings of animal studies, indicate that LH pulsatile secretion and T blood levels are influenced by changes in the state of sexual arousal in human males.