Intravenous doses (100 mg in 20 minutes) of the antidepressant drug nomifensine, administered to male volunteers, increased heart rate and blood pressure, elevated the plasma levels of norepinephrine and its metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG), and powerfully stimulated growth hormone release and inhibited the secretion of prolactin. Oral nomifensine, either as a single 100 mg dose or as a similar dose after 2 weeks' treatment with the drug (150 mg/day), caused none of the above effects. This was in line with the limited (less than 30%) oral bioavailability of the active, unconjugated form of the drug, estimated in the same subjects. MHPG in plasma was slightly but consistently reduced by the 2 weeks' treatment, suggesting reduced turnover of norepinephrine. The observed clinical effects of nomifensine are compatible with uptake inhibition and augmented release of norepinephrine and dopamine and possibly direct agonistic effects on dopamine receptors. Although nomifensine was withdrawn from the market because of immunologic complications, it serves as a model compound of a new pharmacologic class of antidepressants, devoid of many of the disturbing side effects of the tricyclic drugs.