Background: To determine if testosterone levels are influenced by dopaminergic therapy in Parkinson disease (PD) patients. Testosterone level has been reported to be low in patients with PD and other neurodegenerative diseases. In this study, we sought to determine whether dopaminergic therapy (i. e. levodopa and dopamine agonist) influenced testosterone levels. We used a cohort of consecutive male patients from the INSPECT trial--a multi-center, prospective, study that primarily investigated the effects of short-term treatment with pramipexole or levodopa on [(123)I] B-CIT SPECT imaging in early PD.Methods: Testosterone levels were drawn on consenting male subjects with early PD who enrolled in the INSPECT trial at three study visits (baseline, 12 weeks post-treatment, and 8-12 weeks post-washout). Subjects were randomized to: no treatment, pramipexole (up to 3 mg) or levodopa (up to 600 mg). Testosterone levels were obtained twice (prior to 10 AM) and averaged for each of three study visits.Results: Thirty two male patients participated in this sub-study and there were no significant differences in disease characteristics in the 3 groups at baseline. Twenty-nine patients completed the follow-up visits and were suitable for analysis. There were statistically significant differences in the change in free testosterone level, increased in both the levodopa group and pramipexole group but decreased in the untreated group at 12-weeks post-treatment. There were no significant differences in the changes of UPDRS total or motor scores, although there was a strong trend toward improvement in motor scores. The testosterone level persisted in its increase only in the pramipexole group at the end of the washout period.Conclusion: These preliminary data support the premise that dopaminergic medications do not reduce testosterone levels in early PD patients.