To reduce hamodialysis-induced ventricular arrhythmias, each of 15 patients (age 66.9 +/- 6.2 years) with end-stage renal disease and cardiac irregularities was treated subsequently with four different computer-modulated bicarbonate haemodialysis profiles (A-D) for 2 weeks respectively: (A) constant UF, dialysate Na (138 mmol/l) and K (2 mmol/l); (B) decreasing UF, otherwise as (A); (C) decreasing UF and Na (starting with 10% higher than serum Na), otherwise as (A); (D) decreasing UF and Na, adapted K to achieve a maximal reduction of serum K of only 15%/h. Cardiac monitoring was done by 11 h ECG. Only in haemodialysis profile D a distinct reduction of ventricular extrasystoles during and after haemodialysis was obtained. It was accompanied by an improvement in the Lown classification. In addition, a weak but highly predictive correlation between the number of ventricular extrasystoles in the last hour of dialysis and the difference between pre- and post-dialysis potassium concentration in the serum could be established (r = 0.37; P less than 0.004). Computer-modulated potassium profile haemodialysis is a useful tool to reduce the number and severity of ventricular extrasystoles.