The aim of the study was to determine the expression of cytidine deaminase (CDD) gene in bone marrow cells from patients with acute leukemia (AL) and evaluate the relationship between CDD expression and clinical feature. Semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) was used for detection of expression level of CDD mRNA in bone marrow cells from 83 patients with acute leukemia and from 15 healthy peoples as control. CDD/beta-actin ratio >or= 0.5 was considered to be positive. The results showed that expression levels of CDD of 31 previously untreated patients were higher than those of 23 cases of AL in complete remission and of normal controls. Expression levels of CDD of 29 relapse/refractory patients were also higher than those of 23 AL patients in complete remission and of normal subjects. The expression levels of CDD in relapse/refractory ALL were higher than those in AML while expression levels of CDD were not correlated with the outcome of therapy. It is concluded that the level of CDD mRNA expression varies at the different stage of acute leukemia. The expression level of CDD seems not to be a prognostic factor.