The endocrine responses to the 5-hydroxytryptamine (5HT) precursor, L-tryptophan, were assessed in 10 depressed patients before and after at least 4 weeks of treatment with amitriptyline. Overall, amitriptyline did not alter either prolactin or growth hormone responses to L-tryptophan. When three subjects with severe pretreatment weight loss were excluded, however, the remaining seven patients showed a significant increase in the prolactin response to L-tryptophan, consistent with other published studies. The findings suggest that severe recent weight loss may alter the effects of tricyclic antidepressants on 5HT-mediated prolactin release.