Between 1979 and 1985, 26 patients on continuous ambulatory peritoneal dialysis had 97 episodes of peritonitis. These occurred over a period of 336 patient months, giving an incidence of one episode every 3.5 patient months. The micro-organisms comprised Gram-positive and Gram-negative bacteria as well as fungi which accounted for six episodes. Gram-positive bacteria were isolated in 49 of the 97 episodes (50.5%) with Staphylococcus epidermidis predominating. The incidence of culture-negative peritonitis was high (27.8%). Because of failure to respond to treatment, or because of frequent recurrences, 42% patients were transferred to haemodialysis. The changing bacterial ecology has necessitated an alteration in choice of antibiotics. Cefamandole and/or gentamicin are no longer appropriate since 46% strains of S. epidermidis are now methicillin-resistant. Our 'best guess' choice for bacterial peritonitis would now start with netilmicin, vancomycin being added if indicated. For fungal peritonitis we would now start with a primary course of anti-fungal agents followed by early removal of the catheter if there is no response to treatment.