OBJECTIVE The effect of rituximab on B cell and immunoglobulin production after therapeutic apheresis has not been studied in ABO-incompatible renal transplant patients. METHODS Twenty consecutive ABO-incompatible renal transplant patients receiving rituximab induction and double filtration plasmapheresis were enrolled; one case was excluded because of repeated plasmapheresis and immunoglobulin therapy (Incompatible group). The B cell count of the Incompatible group was compared to another group of 18 ABO-compatible renal transplant patients who were operated on during the same period (Compatible group). In the Incompatible group, the total IgM, IgG, and IgG1-4 subclasses after transplantation were compared to those before desensitization. Tacrolimus, mycophenolate mofetil, and steroids were used for both groups. RESULTS The B cell count of the Incompatible group was significantly lower than the Compatible group post-transplant from Month 1 to Month 11 only. The B cell count of the Compatible group also decreased for the first 6 months, suggesting that maintenance immunosuppressive agents suppress B cells. Total IgG and IgM levels after transplantation were significantly lower than before desensitization during the 24-month follow-up period. The post-transplant IgG3 level was significantly lower than before desensitization for only 3 months. CONCLUSIONS With the aid of tacrolimus and mycophenolate mofetil, rituximab resulted in sustained suppression of B cell count and total IgG and IgM. Among the IgG subclasses, IgG3 was less sensitive to rituximab.