The developmental changes in caffeine elimination were studied in 7 infants aged between 2 1/2 weeks and 6 months. Adult plasma clearance rate of caffeine was achieved at 3 to 4 1/2 months of age. Plasma half-life and elimination rate reached adult levels after 3 to 4 1/2 months and seemed to exceed adult capacity thereafter. No significant changes in apparent volume of distribution were noted. Our data provide some indication of the age in infancy when the low rates of caffeine elimination in the neonate increase to the adult rate.