Flow cytometry analysis of Fas or FasL expression with FITC-conjugated antibodies was performed on T-cell subsets that had been gated according to the double expression of IFN-γ or IL-4 (PE-conjugated antibodies) and CD4 or CD8 (PerCP-conjugated antibodies). (A) Fas expression on all T-cell subsets of ITP patients was not different from that of controls at any study point. (B) Patients' pretreatment expression of FasL was significantly increased (P < .01) on Th1 and Th2 cells compared with both controls and responders to rituximab, but comparable with that of nonresponders. No significant differences in FasL expression were observed on Tc subsets.