Although the presence of physiologic anti-CD95 (Fas, APO-1) autoantibodies in intravenous immunoglobulin (IVIG) preparations is known, the effects of these antibodies in patients with common variable immunodeficiency are unclear (CVID). The aim of the study was to assess the effects of IVIG in Fas expression, activation markers and the subsets of T cells in patients with CVID. We studied 15 cases with CVID and 10 healthy controls with no signs of immunodeficiency. The Fas expression of T cells, activation markers (CD25, CD69 and HLA-DR) and T-cell subsets were analyzed by four-color flow cytometry. We found that the Fas expression of CD3+ T cells in patients was significantly higher than in controls. In addition, there was a significant increase in the Fas expression of CD3+ T cells and CD4+ T cells, and the CD25 expression of CD3+ and CD4+ T cells after IVIG supplementation (P < 0.05). The CD69 and HLA-DR expressions of T cells and CD8+ T cells were not affected by IVIG infusion. Our observation showed that IVIG replacement causes an increase in the Fas and CD25 expressions in patients with CVID. These data suggest that the Fas protein may have an important role in the effects of IVIG for the control of autoimmunity in patients with CVID, as well as in the generation of autoimmune disease. © 2009 Springer-Verlag.