From December 1976 to July 1977 Pseudomonas aeruginosa was cultured from the dialysate of 8 hospital patients on peritoneal dialysis. Seven of the cases occurred within 1 month. The source of the epidemic was a water bath used to preheat the dialysis fluids before start of dialysis. Six patients developed a severe protracted peritonitis with Ps. aeruginosa. Continuous peritoneal dialysis with antibiotics added to the dialysis fluid did not eradicate infection, but after removal of the catheters signs of peritonitis subsided rapidly in all patients. In conclusion, water baths used for this purpose should be replaced by dry-heat incubators.