The University of Florida Movement Disorders Center will be following up the promising results of two preliminary studies of testosterone replacement therapy in male Parkinson's disease patients in a placebo-controlled trial, evaluating both for changes in non-motor and motor function. Parkinson's disease is commonly only associated with motor symptoms including slowness, stiffness, tremor, and disturbances in walking and balance. Parkinson's disease, however, is also commonly associated with non-motor symptoms, including fatigue, depression/mood changes, anxiety, reduced libido, sexual dysfunction, and thinking difficulties. The motor symptoms typically show a positive response to dopamine replacement therapy (e.g., Sinemet), but the response of non-motor symptoms to traditional pharmacological interventions has been less successful. Further, these non-motor symptoms of Parkinson's disease can often be more debilitating than the motor symptoms, adversely affecting the quality of life of these patients. This study will evaluate the effectiveness of testosterone replacement therapy on both motor and non-motor symptoms. The results of this study will help to elucidate the role of testosterone in Parkinson's disease, and may lead to a better understanding of potential new therapies for those suffering with this disease.