The response of rest tremor to single doses of subcutaneous apomorphine and oral levodopa was compared in 20 patients with tremor-dominant Parkinson's disease. In eight of these patients, who were experiencing refractory levodopa-induced fluctuations characterised by disabling tremor, we studied the efficacy of sustained subcutaneous apomorphine. Nineteen patients responded favourably to acute challenges of both apomorphine and levodopa, with abolition of tremor in 10. In three, the response was helpful in confirming the clinical diagnosis. Chronic apomorphine use led to a more than 50% reduction in tremor-filled hours per day. After a mean duration of follow-up of 7.5 months, there was no tachyphylaxis to its therapeutic action. Subcutaneous apomorphine is an effective adjunct in treating patients with resistant, tremor-dominant fluctuations, and may also be helpful in the diagnosis of parkinsonian tremor.