Correlation of intracellular ROS levels with clinical parameters. The mean fluorescence intensity (mfi) of DCFH staining (indicative of ROS levels) in short-term cultured CLL cells was measured as described in “Measurement of intracellular ROS” for 33 patients whose clinical features are shown in Table 2. Cytogenetic abnormalities (A), LDTs (B), percentage of CD38⁺ cells (C), clinical Rai Stage classification (D), and number of treatments for symptomatic disease (E) were determined from patients medical records. The average values and standard errors for the different groups are shown. Tumor cells from patients with more aggressive disease had significantly higher ROS levels, as indicated by the P values in the respective panels.*P < .001; **P < .02. The open circles in panel A represent ROS levels in B cells from 4 normal donors, handled in the same manner as CLL cells.