A slow, continuous infusion of 1000 mug TRH (thyrotropin releasing hormone) over a period of 4 h had a very faint and diffuse short-lasting beneficial effect on a group of 10 depressive patients. This was assessed in a double blind cross-over trial with placebo. The effect was of no therapeutic value. No difference was found between the depressive patients and a control group of normal subjects in TSH response, T3 resin uptake, T4 or free thyroxine index values as a consequence of the TRH infusion.