Aim of this work is an analysis of the clinical and microbiological aspects in 205 peritonitis episodes occurred in 156 patients admitted on peritoneal dialysis from January 1980 to December 1989. The evaluation of causative organisms shows a high prevalence of Gram+ organisms (60% of cases), while Gram- organisms are responsible for 16% of peritonitis episodes and fungi for 4%. No cultural growth was observed in 13% of the cases, while more than one organism occurred in 7%. Peritonitis incidence decreased from one episode every 3.9 patient months during 1980-81 to one every 33.6 patient months during 1988-89. This improvement is especially related to the employment of Y-set connection system and to the sterilization of connection lines by amuchina. From 1984 Y-set was used in each of the new patients admitted on CAPD. After its employment peritonitis incidence decreased from one episode every 6.2 patient months to one every 29 patient months. In our experience vancomycin i.v. proved to be effective and well tolerated. In no case a persistence of infectious disease was observed and no catheter was removed.