To test acamprosate's role as an aid in preventing relapse after detoxification, 296 alcohol-dependent patients entered a prospective, multicentre, randomized, double-blind, parallel comparison of acamprosate treatment consisting of two 333 mg tablets given three times daily for 180 days with matching placebo treatment. Unlike previous studies, acamprosate was prescribed from the start of alcohol withdrawal, rather than after the detoxification process. During the treatment period, 110 patients dropped out. The two treatment groups were balanced with regard to baseline values and reasons for discontinuation. There was no difference between the groups in the severity of withdrawal symptoms as measured by the CIWA-Ar (Clinical Institute Withdrawal Assessment for Alcohol scale). Acamprosate given during withdrawal did not cause unwanted effects. The cumulative abstinence duration (CAD, main end-point) was 19 days longer in the acamprosate treatment group than the placebo treatment group (analysis of variance on ranks, P = 0.0006) and the stable recovery duration, defined as the number of abstinent days between the last relapse into any drinking and the end of the trial, was 16 days longer in the acamprosate treatment group (P = 0.021). Continuous abstinence, estimated by survival analysis on time to first relapse, was achieved by 35% of acamprosate-treated patients and 26% of placebo-treated patients (log rank P = 0.068). The geometric mean of the ratio final/baseline values for serum carbohydrate-deficient transferrin was 0.802 (placebo) and 0.733 (acamprosate) (P = 0.059). The geometric mean of the ratio final/baseline values for serum gamma -glutamyltransferase was 0.496 (placebo) and 0.415 (acamprosate) (P = 0.024) which corroborated the greater abstinence reported by the acamprosate group.