Six normal adult male subjects were administered either luteinizing hormone-releasing hormone (LRH, 500 micrograms, intramuscularly injected) or a saline placebo 10 min before a 40-min laboratory session in which they were exposed to erotic stimuli; subjects attended four such sessions, twice receiving LRH and twice the placebo in a balanced, double-blind, crossover design. Sexual arousal was inferred from degree of tumescence, with penile circumference measured by a mercury-in-rubber strain gauge. Heart rate was monitored continuously, and blood samples were taken periodically and assayed for serum luteinizing hormone (LH), follicle stimulating hormone (FSH), and testosterone (T). Rapidity of onset of erection, maximum degree of erection obtained, and overall levels of tumescence were consistently greater following LRH administration than following saline placebo; however, the differences were not statistically significant. The anticipated LH and FSH response to LRH was noted as well as a small increment in LH levels following erotic stimulation. No significant alteration in serum testosterone was observed within the time sampled. There were no significant correlations between hormonal data and any measurement of penile tumescence. In view of the results, further investigation of the behavioral effects of LRH appears justified.