Slow downtitration as a methadone discontinuation method is time-consuming and associated to high dropout rates. Whereas ultra-rapid opiate detoxification methods have recently gained some popularity, they are expensive and may be associated with particular problems in methadone patients. In the present study, a 3-day detoxification procedure accelerated with a unique dose of naltrexone was used in 10 methadone-substituted patients. Whereas the treatment resulted in a shortened withdrawal syndrome, which was satisfactorily controlled by the drugs used, a two-phase course was observed, some symptoms reappearing between the end of day 2 and the beginning of day 3. The first phase of withdrawal symptoms was attributed to the antagonistic effect of naltrexone, which possibly also improved under the weakening of naltrexone. The second phase of withdrawal symptoms may be related to falling methadone plasma levels