It has been postulated that delta sleep-inducing peptide (DSIP) possesses an agonistic activity on opiate receptors and might be of value in the treatment of withdrawal syndromes. To test this hypothesis, DSIP (25 nmol/kg) was injected intravenously as sole treatment to 67 patients presenting withdrawal symptoms (28 from ethyl alcohol, 39 from opiates). 27 % of the patients were lost or unsuitable for evaluation. From the 49 evaluable patients, DSIP produced a beneficial effect in 48 (22 alcoholics and 26 from 27 opiate addicts), with an immediate onset of action, a good and lasting suspension of the somatic symptoms and signs. Anxiety resolved more slowly, within hours. No major side-effect occurred. DSIP offers a new physiologically-based approach for the treatment of established withdrawal syndrome.