Peritonitis in continuous ambulatory peritoneal dialysis (CAPD) patients is only rarely caused by beta-hemolytical streptococci species. We describe two young children, aged 15 months and 5 years, respectively, who presented an unusually severe course of peritonitis due to group B beta-hemolytical streptococci. This course of the disease showed a strong similarity with neonatal streptococcal septicemia. In neonates, IgG2 deficiency is thought to be partly responsible for the severity of this condition. This may also be true for young children treated with CAPD, since IgG2 deficiency has been established for children.