A search was conducted for hepatitis B antigen (HBAg) in 21 serum and 29 muscle specimens from patients with well documented idiopathic inflammatory myopathy. Although intramuscular vascular granular deposits of immunoglobulin and β1C/1A globulin were present in many of these individuals, HBAg was not detected in the serum or muscle of any of them. Antibody to HBAg was detected in serum samples of 10%, similar to the frequency found in normal controls and other hospitalized patients.