To date there are no data concerning IgG subclasses in children with preterminal chronic renal failure (CRF), although a reduction of total serum IgG, including its major subclasses IgG1 and IgG2, has been demonstrated in patients on peritoneal dialysis (PD). Therefore we studied total IgG, IgA, IgM, and IgG subclasses in preterminal CRF (n = 25), PD (n = 22) patients, and 13 age-matched healthy children and also compared results with age-related normal values previously established in 226 healthy children. While total IgG, IgA, IgM, and IgG 1 were comparable, there was a significant deficiency of IgG2 in children both with preterminal CRF and on PD compared with controls. Moreover, the prevalence of IgG2 deficiency compared with age-related normal values was significantly increased not only in PD but also in preterminal CRF patients. We conclude that there are alterations in serum IgG subclasses in children with CRF, with IgG2 deficiency not restricted to PD, but being present in the preterminal state as well.