Slowly increasing oral doses of L-3,4-dihydroxyphenylalanine (L-dopa) induced at least partial improvement of some manifestations in a series of 28 patients with Parkinsonism. Improvement of performance was graded as modest in four, moderate in four, marked in 10 and dramatic in 10. This was usually sustained for periods up to two years. Evidence of toxicity was signaled by few of the variables monitored. Mental effects included enhanced interest, improved memory, transitory sleeplessness and nervousness. Nausea and vomiting were largely circumvented by slowing of the increases of the daily dose. A peripheral dopadecarboxylase inhibitor diminished the therapeutic dose of L-dopa required and eliminated anorexia and nausea in one case. Neurologic side effects consisted of involuntary movements ranging from fleeting to severe.