Chronic renal failure patients on maintenance hemodialysis (HD) have a number of ECG abnormalities and cardiac arrhythmias. Clinical and experimental data have shown that increased QT dispersion is associated with severe ventricular arrhythmias and sudden cardiac death. Therefore, the aim of this study was to investigate whether the uremic patients receiving long-term HD have increased QTc interval and/or QTc dispersion compared to normal subjects and to evaluate the effect of electrolyte changes between the predialysis and postdialysis phases on these parameters. Forty patients with end-stage renal failure on long-term HD (22 men, 18 women, mean age 44 years) were included in this study. Serum concentrations of K +, Na+, Ca++, Mg++, Cl-, phosphate, urea, creati nine, HCO3 -, and arterial blood gases (PO2, PCO2), together with blood pH, were monitored and QTc intervals and QTc dispersion were measured from 12-lead ECG in predialysis and postdialysis phases. The hemodialyzed patients had an increased predial ysis QTc maximum interval and QTc dispersion compared to normal subjects (480 ±51 vs 310 ±38 msec, p < 0.001 and 61 ±17 vs 42 ±14 msec, p < 0.001, respectively). Both QTc maximum interval and QTc dispersion increased significantly at the end of the HD (480 ± 51 vs 505 ±49 msec p< 0.001 and 61 ± 17 vs 86 ± 18 msec, p< 0.001, respec tively). The serum K+(5.3 ±0.56 vs 3.36 ±0.41 mEq/L, p < 0.001), phosphate (7.19 ± 1.62 vs 3.81 ± 1.02 mg/dL, p <0.001), magnesium (0.87 ± 18 vs 0.75±0.14 mg/dL) and urea concentrations (174 ±22 vs 74 ± 14 mg/dL, p < 0.001) significantly decreased, whereas the Ca++ (2.21 ±0.18 vs 2.47 ±0.24 mg/dL, p < 0.001), HCO3- (15.5 ±3.2 vs 20.1 ±3.4 mmol/L, p< 0.001) concentrations and pH (7.27 ± 1.1 vs 7.43 ± 1.2, p < 0.001) significantly increased after HD compared to predialysis values. There was significant correlation between the QT dispersion increase and serum electrolyte changes (K+, Ca++, and pH levels) (p < 0.05). The association between serum electrolyte changes, acid-base status and QT measurements might provide new insights into the evaluation of the ionic bases involved in inhomogeneous ventricular repolarization.