SUMMARY. The growth hormone (hGH) and prolactin (hPRL) response to insulin induced hypoglycaemia was studied in six alcoholics on two occasions before and after treatment with a single intramuscular injection of fluphenazine (Modecate). On both occasions blood samples were taken at intervals before and after the intravenous injection of soluble insulin (0.1 u/kg body weight). The patients were investigated on the first occasion, 2–7 days after cessation of drinking and they all demonstrated an adequate hGH response. They then received an injection of fluphenazine (Modecate 12.5 mg) and were reinvestigated 1 week later. The hGH response to hypoglycaemia was significantly impaired after treatment with fluphenazine. Basal hPRL concentrations were significantly increased and increased concentrations of hPRL in response to hypoglycaemia occurred after treatment. We conclude that a single injection of fluphenazine (Modecate 12.5 mg) has a marked effect on hypothalamic‐pituitary mechanisms controlling hGH and hPRL rele