Hemodiafiltration (HDF) is usually performed using a dialytic solution (D) containing acetate (A) or bicarbonate (B) and a replacement fluid (RF) containing lactate (L). To clarify the role of buffers in HDF, 11 patients underwent different study periods, each three months long: bicarbonate hemodialysis (BHD = Baseline period); HDF with (A) in D and (L) in RF (first period of HDF); HDF with (A) in D and (B) in RF (second HDF); HDF with (B) in D and (L) in RF (third HDF); HDF with (B) in D and (B) in RF (fourth HDF = BHDF). HDF achieved: 1) an increase in dialytic efficiency (kt/V, 1.28), reducing the time-session (197 min); 2) an improvement in acid-base status (pre-dialytic values in BHDF: pH 7.36; pCO2 39.8 mmHg; HCO3- 21.8 mM/L); 3) better "dry weight" gain (reached in 92.8% of HDF and in 81% of BHD sessions); 4) a significant decrease, in dialytic side-effects (mainly during the third and fourth periods). On the whole, BHDF (HDF done using only bicarbonate buffer) represents an easy and safe technique, leading to better cardiovascular stability than BHD and HDF without bicarbonate buffer.