454 patients were treated with quassia tincture for head lice. At examination one week later only three patients had hatched lice. There was firm evidence that these patients had been reinfested. The treatment procedure was acceptable both to patients and to staff and no side-effects were observed. As resistance to clophenothane has appeared, alternative cures are needed. This study confirms earlier reports on the effectiveness of quassia tincture, which seems to be a useful alternative to clophenothane. At present the recommended treatment is two applications with an interval of one week.