We used flow cytometry to analyze the expression of vascular endothelial growth factor (VEGF) on leukemic cells of 11 B-CLL patients using a monoclonal antibody directed against the 121 and 165 isoforms. All patients tested displayed a positive reaction for VEGF. Interestingly, mean fluorescence intensity (MFI) of cases with a progressive pattern of disease was higher than MFI of patients with stable disease. Cellular VEGF-expression may be involved in disease progression.