Cytomegalovirus (CMV) infection is relatively frequent and severe in immunosuppressed patients giving rise to diagnostic and therapeutic problems. We describe a series of 7 patients, six with acute lymphoblastic leukemia and one with aplastic anemia. All patients had CMV infection at the moment of maximum immunodepression. Two patients had undergone recent bone-marrow transplant. Six had been transfused in the two months prior to the onset of infection. Diagnosis was established through isolation of CMV from blood or serological methods. Symptoms ranged from prolonged fever to multi-organic involvement. Two cases had pulmonary involvement as well as fever, hepatitis and petechial rash. Two other cases presented with fever and hepatosplenomegaly and in the remaining, 3, fever was the only sign. Clinical course was favourable in all cases including the two with pneumonitis; of these two the first received acyclovir and anti-CMV Ig and the other received no specific therapy. One of the remaining cases was also given acyclovir and specific anti CMV Ig was administered to the 3 patients with isolated fever. In conclusion, CMV infection should be suspected in immunosuppressed patients with prolonged fever.