Streptococcus agalactiae typically induces serious infections in pregnant women and newborns. Nonpregnant adult patients can also be infected and mortality rate exceeds 40%. CAPD peritonitis is very rarely induced by S. agalactiae. Seven cases have been described previously and all had a very severe course, which included bacteremia, septic shock and death. A 27-year-old male with end-stage renal disease due to membranoprolipherative glomerulonephritis type I, who was on CAPD for 17 months, was admitted with the clinical and laboratory picture of CAPD peritonitis. Severe abdominal pain, shaking chills and fever 38.5 microC were also observed at presentation. Streptococcus agalactiae was isolated from the peritoneal fluid and blood culture was sterile. Under treatment with ceftazidime and tobramycin (i.p.) and vancomycin (i.v.) cultures became negative after 48 hours, abdominal symptoms resolved after 12 days and WBC count in the dialysate normalized after 14 days. As a possible source of infection the patient's partner was shown to be a vaginal carrier of a clone of S. agalactiae identical to that isolated in the peritoneal fluid. S. agalactiae is a rare cause of CAPD peritonitis with potentially very serious consequences. Anal or genital tract colonization is, in general, the source of contamination with S. agalactiae. The microbiological findings in the case presented here suggest that colonization of the patient or of his close environment may be important in the pathogenesis of S. agalactiae-induced CAPD peritonitis.