The purpose of this paper was to estimate the best method of CMV diagnosis in leukemic patients. Materials from 9 patients (serum, heparinized blood and urine) were investigated by serological methods (ELISA and Western blot), for the presence of specific antigens and virus capable of replication, and also by genetic methods (hybridization and PCR). It seems, that the best method for CMV diagnosis in leukemic patients is hybridization performed in quantitation variant, and that DNA CMV level of approximately 20 pg/ml of blood was not linked to symptomatic infection.