An increasing number of patients are prescribed a continuous-cycling regimen because standard manual peritoneal-dialysis exchanges alone are not sufficient in achieving adequate dialysis as defined by the Dialysis Outcome Quality Initiative. Consequently, the number of patients on continuous-cycler therapy is increasing. There is controversy as to whether there are differences in the development of peritonitis between patients maintained on manual therapy and those on continuous cycling therapy. As a result, we retrospectively reviewed the charts of all cycler peritoneal dialysis (CPD) patients maintained on either manual peritoneal dialysis (Baxter UltraBag; Group I) or continuous cycler peritoneal dialysis (Baxter HomeChoice Cycler; Group II) between 1 June 1994 and 31 December 1996. A total of 239 patients were in Group I and 106 in Group II. Both groups were similar in age, race, gender, and presence of diabetes mellitus, coronary artery disease, peripheral vascular disease, and gastrointestinal disease. There was no difference in the overall rate of peritonitis between the two groups of patients [1 episode in 10.4 patient-months (Group I) vs. 1 in 10.0 patient-months (Group II); -0.01843 to 0.02619]. The rates of Staphylococcus aureus peritonitis [1 episode in 48.5 patient-months (Group I) vs. 1 in 141.8 patient months (Group II); -0.06152 to -1.1689]; polymicrobial peritonitis [1 episode in 278.8 patient-months (Group I) vs. 1 in 1134 patient months (Group II): -0.0079 to -0.0478], and fungal peritonitis (1 episode in 202.7 patient-months (Group I) vs. no episodes (Group II); 0.00202 to 0.00785] were significantly lower among patients maintained on the Baxter HomeChoice Cycler. The rate of gram-negative peritonitis was higher among patients maintained on the Baxter HomeChoice Cycler, but this difference was not statistically significant [1 episode in 82.6 patient-months (Group I) vs. 1 episode in 45.4 patient months (Group II); 0.4723 to -0.0248]. We conclude that individual rates of peritonitis were different for patients maintained on either manual or continuous CPD therapy, while the overall rate of peritonitis was found to be similar for both groups of patients. The finding that there may be a difference with the gram-negative peritonitis rate is important since gram-negative peritonitis has been shown to have a more severe outcome in terms of morbidity, mortality, and patient dropout from CPD therapy. A larger, randomized, multicenter study comparing the rates of gram-positive, gram-negative, fungal, and polymicrobial peritonitis is warranted.