The pharmacokinetics of intravenous and oral nadolol, a long-acting beta-adrenoceptor blocking agent, were investigated in six children receiving the drug for treatment of supraventricular tachycardia. In the youngest patient (age 3 months), no distribution phase was seen. In children younger than 22 months of age, nadolol is more rapidly eliminated (t1/2 = 4.3 hours or less) than in older children, in whom elimination is more similar to that in adults (t1/2 approximately 7.3-15.7 hours). After intravenous administration, nadolol displayed two-compartment pharmacokinetics with a distribution phase (t1/2 = 0.2-1.1 hours) followed by elimination. Large changes in nadolol pharmacokinetics may occur during the first year of life. Nadolol should be used cautiously in infants.