Electron microscopy of 57 needle biopsies from livers of 55 patients with chronic hepatitis, mostly of type B, revealed, in addition to typical hepatitis B virus nucleocapsids in 34 cases, also atypical intranuclear inclusions in 9 biopsies. These inclusions consisted of electron-dense particles similar in size to hepatitis B virus nucleocapsids. The possibility of an involvement of a hepatitis non-A non-B virus is discussed.