Previous studies of the effects of age on the disposition of propranolol have produced variable results. We evaluated the stereoselective disposition and protein binding of propranolol enantiomers in 10 young (mean age, 28 years) and 10 older (mean age, 64 years) healthy subjects. After receiving racemic propranolol orally for 6 days, the oral clearances of d-propranolol and l-propranolol were lower by 13% and 17% in the older group compared to the young group, but these differences were not statistically significant. The older subjects had higher alpha 1-acid glycoprotein concentrations (p less than 0.05) and lower unbound fractions of l-propranolol (p less than 0.05). After protein binding was accounted for, the unbound oral clearance of each enantiomer was similar in both groups. l-Propranolol was more highly protein bound than d-propranolol (p less than 0.05) in both young and older subjects. The unbound oral clearance d/l ratio was not different from unity in either group, indicating that the stereoselective differences in oral clearance were largely attributable to the stereoselective differences in protein binding.