The kinetics of amiloride was investigated in plasma, urine, faeces and tissues of rats after oral (10 mg/kg) and i.v. (10 mg/kg bolus and 35 microg/h for 4-days infusion) administration. Initially the experimental data were analyzed by a multiexponential model, then a compartmental model was developed to describe the drug kinetics in plasma, urine, faeces and tissues after the i.v. bolus and the oral administration simultaneously. Aim of the model was also to predict the drug kinetics in plasma and tissues of rats after continuous i.v. infusion. The results of the prediction and the discrepancies between prediction and observed data allowed a deeper insight into the pharmacokinetics of amiloride.