The effect of zimelidine, a specific serotonin-reuptake inhibitor, on alcohol intake was tested in 13 healthy male, nondepressed heavy drinkers who were randomly allocated to receive zimelidine or placebo in a double-blind, crossover experiment. There were five 2-wk experimental periods (baseline, placebo 1 and 2, and zimelidine 1 and 2). Treatment was discontinued in three subjects due to a suspected adverse reaction and three other subjects dropped out. Thus, 13 subjects participated in at least two experimental drug periods and only 10 participated in all the periods. In the 13 subjects zimelidine increased the days of abstinence and decreased the daily number of drinks consumed, whereas in the 10 subjects only the number of days of abstinence increased. Subjects did not report aversive alcohol-sensitizing reactions. Spielberger state-anxiety test scores and depression scores (Montgomery/Asberg and Hamilton) were low at the beginning and throughout the study. Our data suggest that zimelidine modifies alcohol intake by a different mechanism than previously tested drugs, possibly by modulating the central neural mechanism that controls drinking of alcohol.