Intranuclear particles of 23-27 nm diameter have been repeatedly demonstrated in the nuclei of hepatocytes of patients with non-A, non-B hepatitis and of experimentally infected chimpanzees; however, their specificity has been challenged since they have also been observed in other pathological conditions and in healthy volunteers. We have conducted an ultrastructural study of liver biopsies from 10 patients with chronic active non-A, non-B hepatitis. The intranuclear particles, which were observed in all patients, were classified according to the aggregation patterns described by De Vos. Eight patients (80%) had particles of type 2. A reevaluation our proceeding data on Delta hepatitis demonstrated that no particles of type 2 were present. These results support the hypothesis that only type 2 particles are markers of non-A, non-B hepatitis
