Two groups of 10 chronically heroin addicted patients who were admitted to the Emergency Ward because of hypoventilation and coma, were treated random- aselectively with naloxone, 3 micrograms kg-1 BW iv, or with physostigmine salicylate 0,04 mg kg-1 BW iv. Patients in both groups completely regained consciousness and breathed spontaneously, regularly and adequately within 10 minutes. One essential difference in the treatment was that physostigmine caused no signs of acute opiate withdrawal, the patients felt fine and stayed for further control, in contrast with naloxone where the patients felt bad and occasionally escaped prematurely from the ward. Another difference is that the beneficial effect of one dose of physostigmine is shorter lived than that of naloxone. Authors emphasise the fact that treatment of heroin overdose in an addict need not jeopardize the patient's well-being by a withdrawal syndrome.