Effect of the caspase inhibitor Z-VAD.fmk on the viability of B-CLL cells. Cells from patients no. 2 and 6 were seeded in 96-microwell plates and incubated for 48 hours either alone or in the presence of aspirin (ASA; 5 or 10 mmol/L) or aspirin with 200 μmol/L Z-VAD.fmk. Z-VAD.fmk was added 1 hour before aspirin administration. Cytotoxicity was analyzed by the MTT method as described in the Materials and Methods and is expressed as a percentage of the viability of control cells at the beginning of the culture. Data are shown as the mean value ± SD of 3 independent experiments. Statistical significance of differences between treatment with aspirin alone or in combination with Z-VAD.fmk was assayed ANOVA (Fisher’s PLSD). *P < .03; **P < .0001.