Patients maintained on chronic peritoneal dialysis (CPD) have been reported to have a variety of abnormalities of humoral immunity, including hypogammaglobulinemia, altered response to vaccination, and selective absence of IgG2. We measured serum immunoglobulin and IgG subclass levels in 22 pediatric CPD patients followed at our institution; 8 patients had low total IgG; 4 of these had low levels of IgG2 and 3 also had low IgG1, but IgG2 levels were detected in all patients. Thus, many pediatric CPD patients may have low IgG, and some may have low IgG1 and IgG2 as a reflection of low total IgG. However, we did not demonstrate a selective absence of IgG2 in these patients.