Two outbreaks of peritonitis caused by a Mycobacterium chelonei-like organism--a previously unrecognized pathogen--occurred among patients receiving intermittent chronic peritoneal dialysis (CPD). In one center, five of 22 patients who had undergone CPD during a one-month period developed peritonitis caused by an M. chelonei-like organism acquired from a single contaminated automated CPD machine. In a second center, five of eight patients who had received CPD during a several-week period became infected, apparently as a result of cross-infection from contaminated machines. Seven sporadic cases of peritonitis due to an M. chelonei-like organism were also found. M. chelonei-like organisms can survive and proliferate in water and are relatively resistant to formaldehyde. Defects in the design of CPD machines and disinfection procedures were identified that may have permitted M. chelonei-like organisms to survive attempted disinfection.