The TRH stimulation test was administered to 10 cocaine and 10 phencyclidine abusers as well as to 10 controls. No subjects had clinical evidence of depression. Significantly more blunting of the response of TSH to TRH was shown in cocaine and phencyclidine abusers compared with that seen in controls. No significant differences in blunting of response were seen between the cocaine and phencyclidine groups.