The pharmacokinetics of butofilolol, a new beta-blocking drug, was studied in 6 healthy subjects. Plasma concentrations and urinary excretion of the unchanged drug were determined after a single 100-mg oral administration, and also during chronic treatment (100 mg/day for a week) and after the last dose. Maximum plasma concentrations were observed 2 to 3 h after drug administration and varied between the subjects (120 to 430 ng/ml). The apparent volumes of distribution were large, ranging between 200 I and 500 I, and the apparent clearances of elimination appeared to be intermediate between 40 and 70 l/h. Drug elimination in the urine (about 4% of administered dose) occurred by filtration, tubular secretion and pH-sensitive reabsorption following a non-linear process. However, pharmacokinetic parameters remained constant during chronic treatment, since urinary elimination of the parent drug was too low to influence its pharmacokinetic profile. In addition, a high correlation was found between plasma levels of butofilolol and the effect of the drug on resting heart rate, while a slight effect on diastolic blood pressure could be discerned.