Potentiation of the cytotoxic effect of mafosfamide by fludarabine. B-CLL lymphocytes from 6 patients were incubated for 48 hours with various concentrations of mafosfamide ranging from 0.25 to 2.5 μg/mL, without (○) or with 1 μg/mL fludarabine (•). Cell viability was determined by the MTT assay as described in Materials and Methods and is expressed as the percentage with respect to control cells at the beginning of the culture. Data are shown as the mean value ± SD of triplicate cultures. Statistical significance of the synergism between fludarabine and mafosfamide was assayed by ANOVA (Fisher’s PLSD). *P < .05.