In a series of earlier studies, an oral dose of 0.5 mg/kg d-amphetamine was administered to 81 patients with schizophrenia and eight normal control subjects. Seven more subjects with schizophrenia received placebo. Blood pressure and pulse rate were monitored before and 3 hours after drug administration. Blood pressure increased in both amphetamine groups, whereas placebo had no effect. However, pulse rate did not change in the schizophrenic group and only increased after 3 hours in normal control subjects as blood pressure began to decrease. Significant negative correlations between systolic blood pressure and pulse rate occurred at 2 and 3 hours, suggesting that the early cardiovascular response to amphetamine is an increase in blood pressure that recruits reflex control of heart rate. Eighteen of these subjects had hypertensive responses. Six subjects received 5 mg haloperidol intramuscularly, and 12 others had their blood pressure monitored until normalization. Haloperidol led to a more rapid decline of some but not all indices of blood pressure, suggesting that amphetamine-induced hypertension may have a dopaminergic component.