The aim of this study was to hormonally evaluate schizophrenic patients on long-term treatment with neuroleptics. Twenty-eight patients (14 men and 14 women) on long-term therapy with different neuroleptics were investigated. Blood samples for prolactin (PRL), growth hormone (GH) and insulin-like growth factor I (IGF-I) were measured, as well as gonadotropins and testosterone in the males. In addition, clinical signs and symptoms of the neuroleptic side effects were evaluated. Seven out of 14 women had elevated PRL and five of the six fertile women in this group had menstrual disturbances. Twelve of the l4 men had normal PRL levels, whereas two had slightly elevated PRL without related symptoms. Four patients had low IGF-I levels, which in one case was combined with elevated PRL. We conclude that PRL levels in schizophrenic patients on long-term therapy with neuroleptics are elevated in about 50% of the women and in 10-20% of the men. Furthermore, irrespective of PRL levels or other hormonal disturbances, some patients on long-term neuroleptic therapy show low IGF-I levels, pointing at a possible interference with neuroleptics on the hypothalamic-pituitary regulation of GH-dependent IGF-I secretion.