The clinical features of 25 cases of cytomegalovirus (CMV) infection complicating hematological diseases were analyzed. These cases did not undergo allogeneic bone marrow transplantation. 21 cases (84%) had a lymphoid tumor including 16 cases (64%) of malignant lymphoma and three cases of adult T-cell leukemia. All patients but one have received corticosteroid or antineoplastic agents before the occurrence of CMV infection. The types of CMV infections were interstitial pneumonia (23 cases), retinitis (2 cases), enteritis (one case), and persistent pyrexia (one case). Nine cases were diagnosed by histopathology and 5 of these 9 cases were discovered as having a CMV infection at autopsy. 20 cases were treated with ganciclovir for CMV infection, but only 9 cases improved. Of the 9 cases diagnosed by CMV-antigenemia, which had been introduced in the late 1994, 4 cases whose lymphoid tumor had been controlled responded to ganciclovir and survived but others with uncontrollable disease died. The present study indicates that the progress in the treatment of CMV infection was achieved in patients with controllable hematological disease but not in patients with refractory disease even after introduction of CMV-antigenemia.