In order to define more accurately the role of multidrug resistance (MDR)-related protein (mrp) gene in chronic lymphocytic leukemia (CLL), we addressed the question of its expression pattern in isolated peripheral blood B lymphocytes in seven healthy donors and 28 patients with CLL, with respect to some laboratory and clinical parameters of the disease. For this purpose, we used a semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR), based on the coamplification of an internal standard not homologous to the DNA target to quantify the mrp transcription level in each studied sample. We report that the level of constitutive mrp gene's expression in peripheral blood lymphocytes is higher in CLL patients than in healthy controls. We found increased mrp gene expression levels in patients with higher white blood cells (WBC) and lymphocytes' counts as well as in more advanced disease stages according to Rai or Binet scale. Finally, mrp gene's expression was higher in patients with progressive CLL, especially in cases refractory to chemotherapy salvage. The results of the present study suggest that expression of mrp gene might be relevant in the pathogenesis of the MDR phenotype in CLL.