Background: Addition of hyaluronan (HA) to the dialysis solution has been suggested as a means to protect the peritoneum from injury during peritoneal dialysis (PD). Methods: Concentrations of inflammatory mediators were determined in dialysate samples obtained from PD patients after 6-hour dwells with glucose-based (13.6 g/l) solution containing 0.1 and 0.5 g/l of exogenous high-molecular-weight HA. We additionally evaluated the effect of HA-supplemented dialysate, drained after dwell in PD patients, on function of human peritoneal mesothelial cells (MC) in in vitro culture. Results: Concentration of nitrites was significantly higher in HA 0.5 g/l supplemented dialysate (+43%, p < 0.05) as compared to control. Levels of monocyte chemoattractant protein (MCP-1), soluble intercellular adhesive molecule (s-ICAM), vascular endothelial growth factor (VEGF) and fibronectin were comparable in all the studied groups. However, when MC were exposed in in vitro conditions for 24 h to the studied dialysates, we observed that HA containing fluids inhibited the synthesis of MCP-1, s-ICAM, VEGF and fibronectin in these cells. HA-supplemented dialysate accelerated growth rate of in vitro proliferating MC. Conclusion: High-molecular-weight HA added to the dialysis fluid exerts anti-inflammatory and antifibrotic actions on the in vitro cultured MC and accelerates their growth rate what may be important for peritoneal healing during PD.