Abstract The sleep pattern and the plasma concentration of growth hormone were determined during afternoon naps of seven healthy young subjects after i.v. treatment with 3.5 mg haloperidol. The latency of sleep onset and the period in stage 2 were reduced, but the time spent awake was increased compared to control conditions. The magnitude of the sleep induced peak in growth hormone concentration was not modified in five subjects. In two subjects it was abolished as a consequence of shortened sleeping time and disturbed sleep. It is suggested that unlike growth hormone secretion induced by endocrine or metabolic factors, that occurring during sleep is not mediated by a central dopaminergic neuronal pathway.