Thirty-two patients with fever of unknown origin, weight loss, anemia, elevated serum levels of alkaline phosphatase and/or lactate dehydrogenase were evaluated. Histopathologic findings of the liver showed T-cell infiltration in the hepatic sinusoids and portal tracts. The cellular morphology varied from mature lymphocyte to malignant lymphoid cells. We divided the cases into four groups on the basis of cellular atypia. Group A and group B showed mature lymphoid cell infiltration, however, only group B had multiple large areas of hepatocellular necrosis. Group C showed atypical lymphoid cell infiltration. In group D, definite malignant lymphoid cell infiltrates were demonstrated. Groups B, C, and D patients had a very poor prognosis. All of them died despite chemotherapy. Group A patients had a better prognosis. Those who had chemotherapy achieved a complete remission. Progression to a higher group occurred in two of six patients with group B lesions and one of seven patients with group C lesions. The EBV-RNA genomes were found increasingly in the higher groups. This study supports the concept that these groups of disease represent a spectrum of peripheral T-cell proliferations.