Cardiovascular diseases are frequent complications of end-stage kidney disease. The aim of the present study was to prove the arrhythmogenic effect of dialysis using signal averaged ECG. The ECG changes and laboratory parameters (sodium, potassium, urea and creatinine levels) were detected during hemodialysis treatment in 26 patients suffering from end-stage kidney disease. The tests and the ECG were performed four times, before (0. minute), during (at 15 and 90 min), and eventually after dialysis (at 240 min). The duration of the QRS complex, high-frequency low-amplitude signals (HFLA), and root-mean-square voltage of the terminal 40 ms of the filtered QRS (RMS) were determined. We considered test results to be positive when two of the three tested parameters were outside the normal range: QRS > 120 ms, RMS < 20 uV, HFLA > 39 ms. Signal averaged ECG was positive in two cases (8%) before and after the dialysis. The duration of the QRS-complex increased significantly during the dialysis (predialysis: 109 +/- 7.6 ms, postdialysis: 116 +/- 8.0 ms, p < 0.0001). Serum urea nitrogen (predialysis: 26.2 +/- 5.4, postdialysis: 11.4 +/- 3.3 mmol/l, p <0.0001) and serum creatinine levels (predialysis: 931 +/- 212, postdialysis: 434 +/- 120 micromol/I, p < 0.0001) decreased significantly during the treatment. Significant and continuous decrease in the potassium levels were detected (predialysis: 5.30 +/- 0.72, postdialysis: 3.91 +/- 0.42 mmol/I, p < 0.0001) during the dialysis. Serum sodium levels (predialysis: 139 +/- 2.7, postdialysis: 141.4 +/- 2.2 mmol/I) had not changed during the dialysis. A significant negative correlation was found between decreasing potassium levels and increasing QRS duration (r = - 0.48, p = 0.01). Our results support our primer assumption that the metabolic changes during dialysis treatment can lead to considerable risk of cardiac arrhythmias.