The lack of specific information on the peritoneal-function consequences of late peritonitis episodes, and the concern about long-term consequences of peritoneal dialysis (PD), have prompted us to study the peritoneal function of long-term PD patients after a late peritonitis episode. The question is: Is the peritoneum more vulnerable to infections, in terms of functional effects, after a long time on PD? Forty-nine patients observed from baseline to the first year of PD with no peritonitis constituted the "early" control group; 31 other patients had one episode of peritonitis in the same period. Twenty-seven patients with no peritonitis from the fourth to fifth years comprised the "late" control group; 15 other patients had one episode during the same period. The results presented here suggest that peritoneal vulnerability to infectious episodes depends on the PD stage in which they appeared. Certainly, episodes with similar aggressive capacity in terms of inflammation duration (3-4 days) happening during the fifth year led to a loss of ultrafiltration (UF) capacity that does not appear in patients who suffer an episode during the first PD year. A remarkable feature is that this UF-capacity decrease is not accompanied by the usual creatinine mass transfer coefficient increase. This fact suggests that the dependence between peritoneal-glucose-gradient maintenance and water transport has been partially modified over time on PD. In conclusion, late mild peritonitis has distinct peritoneal-function consequences relative to early peritonitis. Patients who continue PD after one late episode showed an accentuation of the usual change which happens on long-term PD, the loss of peritoneal ultrafiltration capacity.