The objective of the work was to evaluate the frequency and time of incidence of cytomegaloviral (CMV) infection and disease in patients after allogeneic bone marrow transplantation (BMT). One hundred patients were followed up (70 with a related and 30 with an unrelated donor), who had transplantations during the period between XI/1996-XI/2000. METHODS nested-PCR (MIE-gene) and antigenaemia (antigen pp65). Active CMV infection was proved in antigenaemia > or = 5 positive cells or in two consecutive positive PCR. The CMV syndrome was assessed in confirmed CMV infection and otherwise inexplicable febrile conditions and/or a drop of haemogram values. For the diagnosis of CMV pneumonia the clinical picture was needed, evidence of active CMV infection and on the X-ray of the lungs interstitial pneumonia. In 33 patients both methods were used, in 67 only PCR. The first positive test appeared 6-321 days after BMT (median +/- 49 days). CMV infection was proved in 44% cases, CMV syndrome in 30% and CMV pneumonia in 4%. In patients with a related donor CMV infection was found in 34.3%, CMV syndrome in 22.9%, CMV pneumonia in 1.4%. After unrelated donor BMT CMV infection was recorded in 66.7%, CMV syndrome in 46.7% and CMV pneumonia in 10% patients. Two patients died from CMV pneumonia. CMV pneumonia was diagnosed 57-115 days after BMT (median +/- 68 days. The risk of CMV infection is high in both groups of patients, in particular in patients after unrelated donor BMT (66.7%). As far as the development of CMV pneumonia was concerned, the mortality in the authors' group was 50%.