It is important to detect liver involvement in extranodal lesions in malignant hematologic disorders to make accurate diagnoses and estimate their clinical stage. We report seven cases of malignant lymphoma and a case of histiocytosis X. All patients expressed positive C-reactive protein and a high erythrocyte sedimentation rate, and a high serum value of alkaline phosphatase or lactic dehydrogenase was seen. Image analyses revealed enlarged livers without any space-occupying lesions. Peritoneoscopy with liver biopsy showed a diffuse presence of white maculae or peliosis hepatis on the liver surface among all the patients, and granulomas with or without malignant cells were observed histologically and congestion was seen in the lobules. Thus, peritoneoscopy with liver biopsy appears to be a useful tool not only to detect early liver involvement in malignant hematologic disorders but also to make their accurate diagnosis.