Isolated renal tubules were prepared from newborn and adult Sprague-Dawley rats. They were used to study the uptake and accumulation of the beta-amino acid, taurine, by renal epithelium. Initial rate as well as steady-state kinetics were studied. Initial rate studies revealed heterogeneity of uptake in newborn and adult tubules. Slower uptake was present in the newborn in the low-affinity system. Slowed efflux was found in neonatal tissue. Newborn tubules in contrast to adult tubules demonstrated uptake under anaerobic conditions. Adult and newborn tissues showed decreased uptake of taurine when incubated with beta-alanine. Physiologic taurinuria, be it in the rat or man, may be due to less rapid initial uptake and/or efflux from ren in neonatal tissue. Newborn tubules in contrast to adult tubules demonstrated uptake under anaerobic conditions. Adult and newborn tissues showed decreased uptake of taurine when incubated with beta-alanine. Physiologic taurinuria, be it in the rat or man, may be due to less rapid initial uptake and/or efflux from ren in neonatal tissue. Newborn tubules in contrast to adult tubules demonstrated uptake under anaerobic conditions. Adult and newborn tissues showed decreased uptake of taurine when incubated with beta-alanine. Physiologic taurinuria, be it in the rat or man, may be due to less rapid initial uptake and/or efflux from renal epithelium.