Two homosexual men were initially seen with polymyositis as the only manifestation of the acquired immunodeficiency syndrome (AIDS) retrovirus infection. They developed AIDS-related complex a few weeks later and typical AIDS two to six months after onset of muscle weakness. By use of anti-human T-cell lymphotropic virus type III antiserum and monoclonal antibodies to lymphocyte subsets in an immunofluorescence technique, viral antigens were found in the OKT4-positive lymphoid cells surrounding muscle fibers and invading the endomysia septa. We concluded that an initial infection with the AIDS retrovirus can be associated with polymyositis, which may be the first clinical manifestation of an impending AIDS-related complex or AIDS.