CQA 206-291, a new ergot derivative with a “biphasic” dopaminergic profile, was studied in 6 patients with longstanding Parkinson's disease suffering from pronounced fluctuations in hourly mobility. On alternate days, up to seven single doses, escalating from 0.2 to 20 mg, were given as replacement for the usual first morning dose of levodopa. At the most effective dosage, four of the six patients obtained as good a peak response to CQA (8-20 mg) as to L-dopa. Side effects were common and similar to other ergot derivatives, suggesting that the initial weak dopamine antagonist properties of the parent compound, documented in animals, may be of little clinical significance. However, comparative studies will be needed to confirm this suspicion. The addition of domperidone successfully reduced the incidence and severity of side effects. CQA 206-291 has potent anti-parkinsonian properties; further longer-term treatment trials are indicated.