Using psychiatric interviews, sexual and affect rating scales, hormonal studies, and neurologic assessment, the authors assessed the effect of L-dopa treatment on men with Parkinson's disease. Patients demonstrated variable affect changes. Approximately one-half of the patients reported an increased sexual interest that was not related to improvement in locomotor function. Hormonal factors appeared to be involved. The findings suggest that male parkinsonian patients who possess an intact hypothalamic-pituitary-gonadal axis experience increased sexual function related to L-dopa treatment.