11 patients (9m, 2f, median age 59 years) with ventricular ectopic activity of at least Lown grade III received 20 mg N-Propyl-ajmaline-bitartrate (N-PAB) p.o. Plasma concentrations of N-PAB were determined with HPLC from blood samples within 26 hours after administration. An open two-compartment model was used. In 8 patients with normal function of the liver and the kidneys, the median clearance of N-PAB was 6.86 ml/min/kg and the median volume of distribution was 1.56 l/kg. Two patients had a clearly diminished clearance of 1.58 ml/min/kg without obvious impairment of liver or renal function. One patient with chronic glomerulonephritis (plasma creatinine 3.4 mg/dl) had a N-PAB clearance of 2.79 ml/min/kg. None of the Spearman rank correlation coefficients between the pharmacokinetic parameters of N-PAB with age, plasma albumin/globulin-quotient, plasma creatinine and cholin-esterase were significant. All calculated parameters were in the range determined in young subjects. It is concluded that physiological changes with age do not lead to significant changes of the pharmacokinetics of N-PAB. On the other hand in patients with increased levels of plasma creatinine a diminished clearance of N-PAB can be expected. It is also possible that patients without an obvious impairment of liver or renal function may have diminished N-PAB clearance.