The formation of fibrin on peritoneal surface has been related to the appearance of adhesions both, in surgical and CAPD patients. It is known that mesothelial cells have fibrinolytic activity related with t-PA production. We studied plasma and overnight peritoneal effluent (OPE) from 20 CAPD stable patients. Antigenic PAI and t-PA were determined. These values and its correspondent peritoneal saturation indexes were compared to urea and creatinine MTCs, peritonitis incidence, UF capacity, protein losses, Pi, Ca, Na, CO2t, urea and creatinine OPE levels. Plasma t-PA 6.64 +/- 4.68 (2.4-20); Plasma PAI-I 24.8 +/- 17.1 (p < 0.001 in respect to controls) (4-62); OPEt-PA 1.46 +/- 0.95 (0.4-4.6); OPE PAI-I 7.3 +/- 5.6 (0-20.4). Peritoneal saturation ratios were for t-PA 29.6 +/- 21% (6-65) and for PAI-I 34 +/- 32% (7-132). In conclusion our data do not support strong relationship between peritoneal t-PA/PAI system and the functional characteristics of the peritoneal membrane although plasma PAI-I, after an increase in patients at early stages on CAPD, shows a tendency to decrease over time and frequent peritonitis. The values of peritoneal saturation ratios for t-PA/PAI are higher than expected for their molecular weight, which suggests local production. An elevated plasma t-PA levels has been found in older patients.