Glycine uptake by newborn rat renal cortical slices in the presence of 2 mM diamide remained unchanged from control value during incubation times up to 30 minutes. Longer exposure to diamide resulted in decreased net uptake. Kinetic analysis of this phenomenon indicated a noncompetitive inhibitory effect of diamide upon the low-affinity glycine uptake system, whereas glycine uptake on the high-affinity system was obliterated. A similar analysis of the diamide effects on adult tissue indicated a noncompetitive inhibition of both the low- and high-affinity glycine transport systems. Diamide did not cause any demonstrable change in glycine efflux from newborn cortical slices. Thus the decreased net uptake we observed in newborn slices in the presence of diamide could be explained solely on the basis of an effect on glycine entry. Simultaneous measurements of intracellular glutathione (GSH) levels in the newborn tissue showed a lack of any direct relationship between the transport effects of diamide and its oxidative effect on reduced glutathione.