In an international double-blind placebo-controlled trial with 493 detoxified alcohol-dependent individuals, ritanserin, a specific 5-hydroxytryptamine, antagonist, was tested in three different dosages (2.5, 5, and 10 mg/day) against placebo over a period of 6 months. Data on changes in mood state, sleep quality, morning vigilance, clinical impression, and social functioning were analysed. None of the three dosages of ritanserin given revealed any significant effect against placebo on the above-mentioned parameters either at the end of treatment or upon relapse. Therefore, we conclude that patients suffering from alcohol dependence without concomitant psychiatric disorders do not benefit from additional treatment with (2.5, 5, or 10 mg/day) ritanserin.