Report of an unusual case of myopathy in an HIV infected patient, responsive only to the immunossupressor drug methothexate. The patient was a 39 year old homosexual male with no past history of HIV-related manifestations. One month prior to admission he noticed that his left thigh was swollen and painful. Two weeks later both arms became enlarged and tender. A few days before admission he noticed intermitent fever and progressive dyspnea. Upon admission, oral thrush, dyspnea and global enlargment of both arms was noted. There was no articular involvement. Fiberoptic broncoscopy revealed Pneumocystis carinii pneumonia (PCP). Serology for HIV was positive. Tests for antinuclear antibodies were negative. Serum CPK level was 1019 IU. Capillaroscopy was compatible with vasculitis. Muscle biopsy revealed multifocal myonecrosis. PCP was successfully treated with standard doses of TMP/SMZ. Although indomethacin, prednisone and dexamethasone were administered in succession, there was relentless progression of myopathy and persistence of fever. Six days after administration of methotrexate, the patient defervesced, volume of arms and legs diminished. CPK levels returned to normal after a second course of methotrexate. Upon reduction of the dose thigh enlargement recrudesced. The patient remained asymptomatic on weekly doses of methothexate. He died five months later of acute respiratory failure.