A growing number of reports have described a myopathy to occur in patients with HIV infection, but the prevalence of HIV-associated myositis is unknown. In this study, patients with elevated creatine kinases (CK) will undergo EMG's and muscle biopsies. Those found to have inflammatory myopathy will be further examined for potential infectious triggers and genetic factors. In addition, the safety and efficacy of prednisone therapy will be tested in a double-blind trial of prednisone vs placebo. To date, 20 patients have had persistently elevated CK levels not explainable by drug abuse, thyroid disease or infectious agents (other than HIV), and have undergone EMG and muscle biopsy. Of those, ten have been found to have polymyositis. The severity of the muscle weakness, and the relatively few side effects we have seen in those receiving prednisone, as well as the rapid clinical improvement and lowering of CK levels, has led us to drop the placebo arm of the study on ethical grounds. We are continuing to evaluate patients with persistently elevated CK levels at the Thomas Street Clinic to increase the number of patients with HIV-associated polymyositis for meaningful clinical and genetic analysis.