Therapeutic trials of intravenously infused thyrotrophin-releasing hormone or melanocyte-stimulating hormone releaseinhibiting factor were conducted in patients with idiopathic parkinsonism. Thyrotrophin-releasing hormone had no consistent effect on extrapyramidal function in five otherwise untreated patients, nor did it significantly modify the response to levodopa in six other individuals. Melanocyte-stimulating hormone release-inhibiting factor exerted a mild amelioratory effect in three of six untreated patients, while in five levodopatreated individuals antiparkinsonian efficacy was potentiated in two and dyskinesias increased in three. In neither group, however, did these effects attain statistical significance.