Liver biopsies from 12 patients with chronic Non-A, Non-B (NANB) hepatitis, 7 with hepatitis B surface antigen (HBsAg) positive chronic liver disease, 1 HBsAg positive normal carrier, and 4 patients with non-viral liver disease, were examined by electron microscopy for cytoplasmic and nuclear changes. Aggregates of particles measuring 20-35 nm in diameter were noted in the nuclei of 8 of 12 patients with NANB chronic hepatitis, but not in the other groups. The tubular changes seen in the endoplasmic reticulum (ER) of chimpanzees with NANB hepatitis were not noted in biopsies from any of our patients.