Apomorphine in combination with a peripheral dopamine receptor blocker (domeperidone) was administered to four parkinsonian patients in a double-blind placebo-controlled study. The therapeutic efficacy of apomorphine was not reduced by domperidone, while nausea, drowsiness, sedation, and arterial hypotension were prevented. Combination of domperidone with dopamine agonists may result in more effective treatment of Parkinson's disease.