We present an interim report of an ongoing, single-blind study of the effectiveness and safety of bromocriptine mesylate (Parlodel) in 15 patients, 14 of whom had severe idiopathic Parkinson's disease (Stages 4 and 5 on the Hoehn and Yahr Scale). The patients had never received levodopa, amantadine, or bromocriptine. Gradually increasing doses of bromocriptine were assessed: Initial daily dosage was 1.25 mg, with weekly increments of 1.25 mg/day until either the clinical response was satisfactory or a maximum of 15 mg/day was reached. The patients were on no other antiparkinsonian agents, except trihexyphenidyl HCl (Artane). Response to treatment was scored on the Columbia Scale. The patients discussed in this report had been in the study for varying times, ranging from 1 month to 3 years. Only one patient who entered this study dropped out because his response to bromocriptine was unsatisfactory; he had taken the drug for 2 weeks. No serious adverse reactions were noted with the gradually increasing dosage regimen. Response on the whole was very satisfactory; patients improved by at least two stages on the Hoehn and Yahr Scale. Improvement began within 48 h of onset of treatment with 1.25 mg daily. The preliminary results of this study indicate that low-dose bromocriptine as a first-line drug in severe Parkinson's disease is definitely warranted.