The purpose of this study was to investigate the acute changes in endothelin (ET) levels immediately after hemodialysis and to determine whether these changes vary with the use of different membranes and hemodialysis solutions. Ten children were included in the study. Three different hemodialysis sessions were performed on all patients: session 1, acetate-based dialysate and polycarbonate membrane; session 2, bicarbonate-based dialysate and polycarbonate membrane; session 3, acetate-based dialysate and polysulfone membrane. In all cases blood samples were obtained before and after dialysis. Pre- and post-hemodialysis ET levels of the patients with acetate-based dialysate and polycarbonate membrane were 33.68 +/- 11.51 pg/ml and 28.27 +/- 12.85 pg/ml, respectively. The fall in ET levels after this session was statistically significant (P = 0.015). We did not observe a statistically significant change in ET levels in the other sessions. Post-dialysis mean arterial pressure values were significantly lower than the pre-dialysis values in all three dialysis sessions (P < 0.01). A positive correlation was observed between plasma ET levels and blood urea nitrogen and serum potassium; a negative correlation was observed between plasma ET levels and hematocrit.