Twenty uremic patients submitted to three different dialytic procedures (6 patients to acetate dialysis, 8 patients to bicarbonate dialysis, 6 patients to hemofiltration) were monitored in respect to the hemodynamic parameters recorded with a thermistor Swan-Ganz catheter. During acetate dialysis there was an increment of cardiac index (CI) up to positive values (+4.8%), while resistance index (RI) decreased progressively until it reached -16.5%. During bicarbonate dialysis CI, after an initial fall, remained constant and RI increased (+8.6%). During hemofiltration CI decreased constantly throughout the entire procedure while RI increased until +12.9%. We concluded that during diffusive transport the buffer used plays an important role in determining hemodynamic responses to fluid removal; during convective transport vascular resistance increases in spite of acetate.