Adrenergic neurotransmission was studied in dogs. Blood samples for catecholamine assay were collected from the flaccid penis, the erect penis after cavernous nerve stimulation and during detumescence induced by sympathetic trunk stimulation. Epinephrine concentration was not significantly different in these three stages. However, norepinephrine concentration increased significantly (p less than 0.005) during induced detumescence from 505 +/- 311 [pg./ml.] to 747 +/- 489 [pg./ml.]. Intracavernous application of norepinephrine abolished cavernous nerve induced erection in a dose dependent manner. Sympathetic trunk stimulation reduced or abolished erection induced by acetylcholine or by vasoactive intestinal polypeptide. We conclude that norepinephrine is an important neurotransmitter in the control of penile detumescence.