Abstract S-adenosyl- L-methionine (SAMe), a putative antidepressant, is a naturally occurring substance whose mechanism of action is still a matter of speculation. It has been recently postulated that SAMe may increase the dopaminergic tone in depressed patients. Since dopamine inhibits both thyrotropin (TSH) and prolactin secretion, we investigated the effects of treatment with SAMe on the TSH amd prolactin response to thyrotropin-releasing-hormone (TRH) stimulation in 7 depressed outpatient women (mean age: 46.1 ± 7.2 years) and 10 depressed outpatient men (mean age: 38.0 ± 10.0 years) participating in a six-week open study of oral SAMe in the treatment of major depression. At the end of the study, there was a significant reduction after treatment with SAMe in the response of both prolactin and TSH to TRH stimulation in the group of depressed men compared to pre-treatment values. On the other hand, in the group of depressed women, the post-treatment prolactin response to TRH did not appear to change when compared to pre-treatment and the TSH response to TRH challenge tended even to augment slightly after treatment with SAMe. Our results, at least in depressed men, seem to support the hypothesis of a stimulating effect of SAMe on the dopaminergic system.