Twelve patients with unipolar depressive disorders received 600 microgram of synthetic TRH or LRH, in a random order, for 3 days each. Placebo injections were given as two 3-day courses prior to and between the active treatments. Serum TSH, prolactin (Prl) and LH were measured by radioimmunoassays prior to the experiment as well as immediately before and 20 min after each injection. Serum T4 and T3 were determined by radioimmunoassays before the treatments and 24 h after the first two TRH injections. Serum T4 level in depressed patients did not differ from controls. Serum T3 level in depressed patients was significantly below, and the reverse T3 level was slightly above the normal mean. However, the latter difference was not statistically significant due to the large variation of rT3 levels among the depressed patients. The TSH responses did not differ from that of controls after the first injection but the responses after the second injection were lower than in a control study. The Prl responses to TRH were sub-normal in seven out of eight patients. Blunted LH responses to LRH were seen in three patients.