Prostaglandins may be involved in human penile erection and erectile failure. To evaluate the possible role of prostaglandin metabolism in the penile tissue, the activity of nicotinamide adenine dinucleotide-dependent prostaglandin 15-hydroxydehydrogenase was assayed in the corpora cavernosa of the human penis. Km values (mean +/- SD) of the enzyme for PGE1, PGE2 and PGF2 alpha were 60.1 +/- 4.2, 17.7 +/- 1.5 and 16.1 +/- 1.2 microM respectively; Vmax values (mean +/- SD) were 0.219 +/- 0.062, 0.510 +/- 0.012 and 0.424 +/- 0.007 nmol/min/mg protein respectively. The implications of these findings in the erectile process are discussed.