Few studies have assessed the role of pituitary and gonadal hormones on age-related changes in sexual behavior in healthy men. We conducted a retrospective and prospective evaluation of sexual function and behavior in 77 healthy married men aged 45 to 74 years. The subjects were studied in the sleep laboratory for four nights with the last night devoted to sequential blood sampling every 20 minutes. Significant age-related decreases in sexual desire, sexual arousal and activity, and increases in erectile problems were noted. Aging was negatively correlated with bioavailable testosterone (bT), was positively correlated with luteinizing hormone (LH), and was not related to total testosterone, estradiol, and prolactin. Bioavailable testosterone, and the ratio of bT over LH showed a close association with several sexual behavior dimensions while total testosterone, estradiol, and prolactin demonstrated few or no behavioral relationships. The age-related effect of bT was, however, a more important determinant of the reported behavioral differences than were the effect of bT independent of age. There was no evidence that changes in circulating hormones contribute to erectile disorders in healthy aging men.