To assess the efficacy of supervised disulfiram as an adjunct to out-patient treatment of alcoholics, a randomised, partially blind, six-month follow-up study was conducted in which 126 patients received 200 mg disulfiram or 100 mg vitamin C under the supervision of a nominated informant. In the opinion of the (blinded) independent assessor, patients on disulfiram increased average total abstinent days by 100 and patients on vitamin C by 69, thus enhancing by one-third this measure of treatment outcome. Mean weekly alcohol consumption was reduced by 162 units with disulfiram, compared with 105 units with vitamin C, and the disulfiram patients reduced their total six-month alcohol consumption by 2572 units compared with an average reduction of 1448 units in the vitamin C group. Serum gamma-GT showed a mean fall of 21 IU/I in patients on disulfiram but rose by a mean of 13 IU/I with vitamin C. Unwanted effects in the disulfiram group led to a dose reduction in seven patients and to treatment withdrawal in four (and in one vitamin C patient). Two-thirds of the disulfiram group asked to continue the treatment at the end of the study. There were no medically serious adverse reactions.