Tissue distribution of propafenone has been studied in the rat. Measurement of propafenone was made in several tissues: plasma, heart, kidney, lung, liver, muscle, fat and brain, after i.v. administration of 2 mg/kg of the drug. The plasma propafenone kinetics profile can be described by a two-compartmental model. The pharmacokinetic parameters, derived from plasma levels, showed a t1/2 beta of 55.4 min, the central Vd/kg of 2.4 ml/kg, the Cl of 62.8 ml/min.kg and the AUC0-oo of 31.6 micrograms.min/ml. The analysis of the propafenone tissue distribution showed the highest concentration of drug in the lung, followed by the heart and kidneys. A significant concentration was found in brain, muscle and adipose tissue, with concentration ratios (tissue/plasma) above 1. The half-life values obtained for individual organs and tissues are similar to those obtained in plasma, around 1 h. In the post-distributive phase, plasma and tissue concentrations decline in parallel.