Cardiovascular reflexes were evaluated in 18 patients with idiopathic Parkinson's disease who had a Hoehn & Yahr score of III-IV. The effect of apomorphine and domperidone on blood pressure, heart rate, R-R interval variation, and the Valsalva ratio were studied. Autonomic dysfunction was not found in the patients and there were no differences between subgroups of patients on different treatments. Apomorphine altered cardiovascular reflexes to a greater degree in patients who received the drug for the first time than in chronically treated patients. The changes were antagonized by domperidone, a peripheral dopamine receptor antagonist. Apomorphine treated patients who were receiving long-term domperidone had similar abnormalities of cardiovascular reflexes to those who had been able to withdraw it.