An increased rate of obstruction of peritoneal dialysis catheters is observed during peritonitis. Hypercoagulation and hypofibrinolysis may explain this increased occurrence. We studied plasminogen activator inhibitor type 1 antigen (PAI-1), tissue-type plasminogen activator antigen (t-PA), D-dimer (DD), plasmin-alpha2-antiplasmin complexes (PAP), and thrombin-antithrombin III complexes (TAT) in 7 children with peritonitis (group A) and 12 children during stable peritoneal dialysis (group B). Albumin, beta2-microglobulin, IgG, and alpha2-macroglobulin were measured for baseline transperitoneal protein transport. After a dwell of 6 h with 1.36% Dianeal, dialysate and serum samples were collected. Dialysate to plasma ratios of all proteins were calculated. During peritonitis (group A) TAT was higher: 34.7 versus 22.0 (P=0.01). PAI-1 was increased in group A: 76.5 versus 22.9 (P=0.004). PAP was decreased during peritonitis (group A): 24.9 versus 39.3 (P=0.01). In group A, DD were decreased. 10.8 versus 26.7 (P=0.002). t-PA was similar in both groups (23.7 in group A vs. 27.7 in group B; P=0.26). In both groups TAT, PAI-1, t-PA, PAP, and DD were significantly higher than in baseline transperitoneal transport, suggesting intraperitoneal production. Hypercoagulability and hypofibrinolysis were present during peritonitis compared with the control situation.