To clarify the influence of neutral dialysate (ND) on peritoneum, we examined changes in peritoneal permeability and in various markers of the coagulation and fibrinolytic system in effluent and the correlations between peritoneal permeability and those markers in peritoneal dialysis (PD) patients using ND. We evaluated 14 patients (8 men, 6 women; mean age: 58.6 +/- 12.0 years) who started PD using ND. The peritoneal equilibration test (PET) was performed to assess dialysate-to-plasma ratio for creatinine (D/P Cr) as peritoneal permeability. Coagulation markers [thrombin-antithrombin complex, fibrin monomer (FM), prothrombin fragment 1+2 (F1 + 2)] and fibrinolytic markers (fibrin degradation products, D-dimer) in effluent were also measured. At 2 years, FM in effluent was significantly lower (p = 0.006). The other markers and the D/P Cr did not change significantly. At the initiation of PD and at 2 years, D/P Cr was significantly correlated with F1 + 2 (r = 0.70 and 0.76 respectively, p < 0.01). Furthermore, multiple regression analysis showed that only F1 + 2 was correlated with D/P Cr at 2 years (r = 0.79, p = 0.004). These results suggest that ND has little influence on coagulation and fibrinolytic markers in effluent. In addition, F1 + 2 is a useful marker for peritoneal permeability in PD patients using ND.