Liver specimens were obtained from 21 non-A, non-B hepatitis patients when their serum transaminase levels were still elevated. The specimens were investigated by transmission electron microscope in order to investigate the presence of the structure relating to this type of hepatitis. Intranuclear electron-dense aggregates of virus-like particles were observed in 2 out of 21 cases. One was an unresolved acute hepatitis case with short-incubation posttransfusion type, and the other was a chronic persistent hepatitis case without bloodtransfusion. The size of these particles varied from 22 to 28 nm in diameter. The incidence of hepatocytes with the particles was approximately 2 to 3% of the cells investigated. These particles may represent an intranuclear alteration in close association with one type of non-A, non-B hepatitis.