A prospective placebo-controlled, randomized double-blind study of Acamprosate at two dose levels in alcohol-dependent patients followed up for 12 months was performed. After detoxification, each of the 538 patients included was randomly assigned to one of three groups: 177 patients received placebo, 188 received Acamprosate at 1.3 g/day (low dose group) and 173 received 2.0 g/day (high dose group) for 12 months. This was followed by a single blind 6 month period on placebo. The patients' mean age was 43.2 +/- 8.6 years. Their mean daily alcohol intake was high (nearly 200 g/day) and of long duration (9.5 +/- 7.1 years). Abstinence figures followed the order high dose > low dose > placebo. The difference was significant at 6 months (P < or = 0.02) but not at 12 months (P = 0.096). The number of days of continuous abstinence after detoxification was 153 +/- 197 for the high-dose group versus 102 +/- 165 for the placebo group (P = 0.005), with the lose-dose group reporting 135 +/- 189 days. Clinic attendance was significantly better in the Acamprosate groups than in the placebo group at 6 months (P = 0.002) and 12 months (P = 0.005). During the 6-month post-treatment period, no increased relapse rate or residual drug effect was observed. The side effect profile for Acamprosate was good compared with controls with only diarrhoea being reported more frequently (P < 0.01). This study confirms the pharmacological efficacy of Acamprosate and its good acceptability. As an adjunct to psychotherapy, this study supports the inclusion of Acamprosate in a strategy for treating alcoholism.