Terguride is an ergoline derivative with mixed agonistic/antagonistic dopaminergic activity. This led to a paradoxical suggestion that it is effective in the treatment of both schizophrenia and parkinsonism. A total of 65 in- or outpatients with parkinsonism mostly of vascular or idiopathic etiology were included in a 4-week, open, multicenter trial. Terguride was administered under an increasing dose schedule which was leveled off according to the clinical response. Mostly because of nausea, vomiting, and lack of improvement 25% of inpatients and 61% of outpatients were removed from the study. The average daily dose at the end of the trial was 4.2 mg, ranging from 1.0 to 5.5 mg. The average Simpson and Angus scale total score and performance in the Spiral Drawing Task improved significantly during the trial by 20% and 38% respectively. The following adverse effects were noted most frequently throughout the study (including those who withdrew): constipation (occurred in 42% of all ratings performed during the trial) drowsiness and nausea (16% each). Adverse circulatory effects were negligible. Psychotic symptoms, including depression, confusion, hallucinations, and paranoid syndrome, each occurred in 1 patient, i.e., at a lower rate than with other dopaminergic drugs. Scotopic electroretinograms in a subsample of 7 patients showed a significant transitory decrease in the B-wave amplitude at the end of the 1st week and a subsequent return to pretreatment values.