This study was carried out to compare the efficacy of chlormethiazole and chlordiazepoxide in the treatment of acute alcohol withdrawal syndrome in 40 patients. Repeated biochemical, clinical, and psychophysiological measurements were obtained in a randomized, double-blind design in which one group of patients received chlormethiazole and a second group received chlordiazepoxide over a period of 7 days. Analysis indicated both drugs to be of equivalent potency and were equally well tolerated by patients. The more severe aspects of withdrawal were brought under control within the first 4 days of treatment. However, even at 7 days, there still persisted some symptoms attributable to the withdrawal from alcohol.