Continuous ambulatory peritoneal dialysis (CAPD) is now a widely accepted treatment for end-stage renal disease. However, the high incidence of peritonitis is a major complication of CAPD. Polymorphonuclear leukocytes (PMNs) play a major role in antimicrobial response of the host. During phagocytosis, the PMNs undergo a striking increase in oxidative metabolism, known as the respiratory burst, and emit light as chemiluminescence (CL). CL is thus a sensitive measure of PMN oxidative potential and correlates well with antimicrobial activity. In view of the observation of increased susceptibility to infection in CAPD patients, we have studied lucigenin- and luminol-enhanced CL in peritoneal fluids of these patients and assessed the diagnostic accuracy of these tests by ROC curve analysis. ROC curves showed diagnostic accuracies for both tests that were superior to counts of PMNs in the dialysis fluid (P <0.001). At selected cutoff values of 150 000 cpm/vial for lucigenin CL and 600 000 cpm/vial for luminol CL, sensitivities were 100%. Specificities for lucigenin and luminol CL. were 89% and 80%, respectively. Our results suggest that CL measurements can be used as an early marker for the presence of infection in CAPD patients.