The antidepressive efficacy of TRH was investigated in 15 endogenous depressive patients in a double-blind cross-over design. The Hamilton depression scale, the AMP (PAS) system, v. Zerssen scale and thermometer scales were used. No therapeutic effect could be demonstrated. The blunted TSH-response to TRH, which has been described by other investigators, was confirmed. There was suggestive evidence of a psychoendocrinological relationship in the sense that the more severe the "somatic depressive" syndrome as calculated from the AMP system, and the more marked the diurnal variation of the endogenous type is, the lower are the basal TSH-values and the smaller the response to TRH. Thus, TRH may become a useful tool to identify subgroups of depressive patient populations.