Apomorphine is a powerful dopaminergic drug, able to improve cardinal symptoms of Parkinson's disease in few minutes, when injected subcutaneously. We administered different doses of apomorphine s.c. against placebo in 25 patients with a Parkinsonian syndrome, with the aim of discriminating Parkinson's disease from other Parkinsonism. A positive response to apomorphine was predictive (88%) of good responsiveness to levodopa therapy. Our data, together with those of other groups, indicate that apomorphine test is a useful tool in the diagnosis of Parkinsonian syndromes.