A long-term follow-up evaluation on the clinical usefulness of selegiline hydrochloride (selegiline) was performed in 13 patients with Parkinson's disease. All patients, except one case, subjected to the study were symptomatically improved by combination therapy of selegiline with L-DOPA in the preceding short-term evaluation. One patient continued the therapy after an evaluation of no symptomatic improvement in the short-term study, because this patient strongly requested continuation of medication, expecting to stop the progression of the disease. The average daily dose of selegiline at the last evaluation was 6.9 +/- 2.5 mg. The average daily dose of L-DOPA at each evaluation point in the patients who continued the therapy for 12 months remained low compared to that prior to the therapy (before: 450 +/- 117 mg, at the 12th month: 389 +/- 89 mg). In the analysis of individual parkinsonian symptoms, the improvement in the mean score for most of the symptoms, especially the wearing-off phenomenon and frozen gait, persisted for the entire period of study. Global improvement rates (moderately improved) at the 6th and 12th month, and the last evaluation were 61.5%, 44.4% and 46.2%, respectively. Among 13 patients, therapy was discontinued only in one case due to hallucination. Although the global improvement rate declined in the course of the therapy, selegiline seems to be useful for improving L-DOPA responsive symptoms in long-term therapy for Parkinson's disease.