Forty-two schizophrenic patients under chronic neuroleptic treatment (11-24 years) were studied, 20 without and 22 with tardive dyskinetic symptomatology. Blood and urine samples were collected on 3 consecutive days. Plasma prolactin (PRL) and urinary homovanillic acid (HVA) values were higher in both tardive dyskinetic and nontardive dyskinetic groups, compared to normals. The increased PRL and HVA values were not related to tardive dyskinesia but to the actual neuroleptic dose. The subgroup of patients with actual dose under 900 chlorpromazine equivalents had normal PRL values and increased HVA at low significance level compared to normals, while the subgroup with doses over 900 equivalents had highly significant (p less than 0.001) increased PRL and HVA values. Thus, the actual neuroleptic dose determines plasma PRL and urinary HVA excretion in patients chronically treated with neuroleptics.