Ten unselected patients with Parkinson’s disease were treated with MIF alone. In the acute trial maximum improvement occurred 2 h after intravenous infusion. After 14 days of treatment a slight but statistically significant improvement of the entire status was seen. Tremor at rest, facial changes, speech and script reacted most favourably, whereas akinesia and rigidity showed little, if any change. Clinical findings and psychological test results recorded during and after treatment revealed an emotional change by the drug. In patients who improved, mood and drive changed to the positive in contrast to the non-improved, with mood deterioration and increased restlessness. A central effect is assumed which, through an increase in the feeling of well-being, causes the changes in the syndrome.