Plasminogen activator inhibitor-1 (PAI-1) is an important regulator of plasminogen activators and has been shown to be involved in the accumulation of extracellular matrix (ECM) in various tissues. Since peritoneal interstitium is one of the main resistance sites of peritoneal transport, the level of PAI-1 in the peritoneum may have a significant effect on water and solute transport during peritoneal dialysis (PD) via its effect of peritoneal ECM. Therefore, we studied the associations between plasma or dialysate PAI-1 levels and the peritoneal transport during standard peritoneal equilibration test (PET) in 8 diabetic and 8 non-diabetic stable PD patients who were matched for their demographical data. There were no differences in plasma PAI-1 levels and PET variables between these two groups of patients. In each group, there was an increase in dialysate PAI-1 level with dwell time as a result of the diffusion of plasma PAI-1 into peritoneal cavity and the local production and release of PAI-1 in peritoneal tissue. However, the extent of this increase was less in the former. In non-diabetic patients, the change in dialysate PAI-1 amount was a significant positive predictor for the diffusive transports of urea and transport. These results are consistent with the hypothesis that peritoneal PAI-1 has a significant effect on peritoneal transport during PD. Further studies including more patients are needed to confirm our observations, and studies providing more direct evidence are needed to test this hypothesis.