THE NARCOTIC ANTAGONISTS USED FOR TREATING ADDICTION, CYCLAZOCINE AND NALTREXONE, ARE NOT THEMSELVES ADDICTING AND HAVE NO ABUSE POTENTIAL, BUT WHEN ADMINISTERED TO AN OPIOID DEPENDENT PERSON PRECIPITATE THE FAMILIAR OPIOID ABSTINENCE SYNDROME. IF A PERSON IS NO LONGER DEPENDENT ON OPIOIDS, CONSUMPTION OF ANTAGONISTS WILL PREVENT READDICTION, AND, EVEN IF HEROIN IS USED, WILL PREVENT EUPHORIA AND OPIOID DEPENDENCE. IN ADDITION TO ITS BLOCKING ACTION, CYCLAZOCINE PRODUCES ANALGESIA AND DISPHORIC SIDE EFFECTS AND THESE PREVENT ITS LARGE-SCALE CLINICAL USE. IN RESPONSE TO A 1971 CONGRESSIONAL MANDATE TO STUDY ANTAGONIST DRUGS FOR HEROIN TREATMENT, RESEARCHERS SELECTED NALTREXONE FOR EXTENSIVE CLINICAL TESTING. RESULTS INDICATE NO EVIDENCE OF TOXICITY FROM NALTREXONE AND NO FERTILITY OR TERATOGENIC EFFECTS. IN STUDIES ATTEMPTING TO IDENTIFY PATIENT TYPES MOST LIKELY TO BENEFIT FROM ANTAGONIST TREATMENT, PREDICTOR VARIABLES WERE NOT FOUND, BUT IN STUDIES CONDUCTED TO ESTABLISH TREATMENT OUTCOMES OF NALTREXONE AND CYCLAZOCINE, CLIENTS WERE OBSERVED TO BE ABLE TO RESTRAIN FROM FURTHER HEROIN USE AT RATES RELATED TO THEIR TIME IN TREATMENT. THESE AND OTHER STUDIES SUGGEST THAT STUDIES REGARDING ANTAGONISTS SHOULD BE DONE IN THREE MAJOR AREAS: (1) THE PREREQUISITE DETOXIFICATION FROM OPIATES; (2) THE DEVELOPMENT OF NEW ANTAGONIST COMPOUNDS; AND (3) THE TREATMENT MILIEU IN WHICH AN ANTAGONIST IS USED. THE PHARMACOLOGIC ACTIONS OF ANTAGONISTS WHICH PROTECT AGAINST READDICTION MAKE ANTAGONISTS PARTICULARLY WELL SUITED FOR USE WITH INDIVIDUALS WHO HAVE PROGRESSED IN ANOTHER MODALITY. REFERENCES ARE PROVIDED. (DAG) FOR RELATED ARTICLES, PLEASE SEE NCJ 57805-57812 AND 57814-57834.