The comparison of the blood pressures of 273 patients with Parkinson's disease and of controls matched in sex and age revealed that Parkinsonian patients had a lower systolic blood pressure and more rarely suffered from clinical hypertension than did the control subjects. Among the Parkinsonian patients both the systolic and diastolic blood pressures decreased with advancing stages of the disease. The severity of tremor did not correlate significantly with the level of the blood pressure, but with increasing severity of rigidity and hypokinesia the blood pressure lowered significantly.