 While testosterone T has been previously shown to be safe and well tolerated in hypogonadal males, it has not been previously given to male MS patients. This study will determine whether treatment with testosterone T, as a percutaneous gel, is safe and well tolerated in male patients with relapsing MS through the following approach. Patients will be followed clinically and with serological studies 6 months prior to treatment to establish baseline data. Then, testosterone T gel will be administered daily at 100 mg per day for 6 months. Patients will continue to be followed clinically and with serological studies. Toxic effects of T gel treatment will become evident if patients change during treatment as compared to their baseline. To determine if T gel treatment induces a decrease in MS disease activity, the most sensitive measure will be used, the number and volume of gadolinium enhancing lesions and the volume of T2 lesions on serial cerebral magnetic resonance imaging MRI. 12 patients will undergo MRI once a month, for 6 consecutive months, before starting treatment to establish their baseline level of disease activity on MRI. Then these 12 patients will be treated with T gel for 6 months. Patients will continue to undergo serial MRI once a month, for 6 more consecutive months, while on treatment. In this manner, the level of disease activity during treatment can be compared to the level of disease activity before treatment. Patients will also be followed with standard neurological exams every 3 months, however it is hypothesized that, with only 6 months of treatment, no effect of T gel treatment will be observed on clinical disease activity disability, relapse rate since this is a less sensitive measure. Further, to determine whether T gel treatment induces desired effects in the immune system, immune responses will be assessed before treatment and during treatment. Results of in vivo delayed type hypersensitivity and in vitro cytokine production responses will be compared before treatment with those during treatment. Finally, since T gel therapy at this dose of 100 mgday has been shown to improve sexual function and mood, increase lean body mass and strength, decrease body fat and increase bone mineral density, we will monitor whether these positive effects also occur in men with MS during treatment. 