PURPOSE:The purpose of this study was to assess the effect of long-term and differing frequency of on-line hemodiafiltration (OL-HDF) on changes in degree of hemoglobin, albumin level, serum small and middle molecules concentration in stable patients with undergoing high-flux hemodialysis (HF-HD). METHODS:Twenty five patients with more than 3 months of HF-HD were divided into two groups and followed for more than 36 months. Group 1 was treated once with OL-HDF and twice with HF-HD per week. Group 2 was treated three times with OL-HDF per week. Analysis was performed to compare hemoglobin, biochemical parameters, serum beta-microglobulin, leptin, alpha-microglobulin levels in both groups. RESULTS:There were significant improvements in hemoglobin and albumin level in group 2 compared to group 1. After receiving OL-HDF for a mean of 24 months, patients on both groups had the significantly reduced predialysis level of beta-microglobulin compared to baseline level. However, there is no significant difference in beta-microglobulin level between both groups. The predialysis level of leptin and alpha-microglobulin with relatively large molecular weight was not significantly reduced during observational period and was not significantly different between both groups. CONCLUSION:There were improvements in hemoglobin and albumin level according to the frequency of OL-HDF. The predialysis level of beta-microglobulin was significantly reduced after receiving even once with OL-HDF per week for long-term. Therefore, our study can suggest that there is no correlation between the frequency of OL-HDF and the predialysis level of beta-microglobulin.