A multicentre, randomised, double blind treatment trial was set up comparing imipramine (a tricyclic antidepressant with anticholinergic action), mianserin (a quadricyclic antidepressant without anticholinergic activity), and placebo, (a) possibly to identify an effective alternative drug and (b) to elucidate the action of imipramine in enuretic children. Eighty children (65 boys, 15 girls) aged 5-13 years, wet three or more nights a week, were studied. Exclusions were a urinary tract infection or abnormality, other organic illness, or severe emotional disorders. After a four week assessment, 25 children were randomised to eight weeks' treatment with imipramine 25 mg, 26 to mianserin 10 mg and 29 to placebo, followed by four weeks without treatment. Dry nights and a wetness score were recorded throughout. During treatment, imipramine was superior to both placebo and mianserin (p < 0.001) in achieving dry nights and reducing wetness scores. It led to a definite improvement in 72% of children. Mianserin produced a mildly beneficial effect that was not superior to placebo. No side effects were recorded. Mianserin would not be a satisfactory alternative treatment for nocturnal enuresis. The efficacy of imipramine is unlikely to be the result of its antidepressant activity.