Using C-labeled amino acids, absorption of L-lysine, L-arginine, L-glutamate, L-phenylalanine, L-methionine, L-threonine, L-alanine, and L-glycine were studied. All amino acids appeared to be absorbed by both simple diffusion and mediated systems. Inhibitions produced by analogues indicate 5 possible transport loci. Locus A may have 3 Bites, one which transports lysine and the remaining 2 binding glutamate and arginine. When occupied, the latter 2 appear to stimulate the transport of lysine. Methionine and phenylalanine were shown to bind nonproductively at the lysine transport site. Locus B transports threonine, glycine, and alanine with negligible interaction with the other amino acids studied. This locus is partially Na+-sensitive. Locus C transports glutamate primarily. Locus D has 2 transport sites, one for phenylalanine and one for methionine. Threonine shows slight interaction at this site. Locus E also has 2 transport sites, one for lysine and one for arginine. All 8 amino acids were tested for Na+ sensitivity, with only the amino acids entering at Locus B affected. Further evidence for Na+ sensitivity of Locus B was demonstrated in that the uptake of threonine, glycine, and alanine was ouabain-sensitive. The uptake of methionine and phenylalanine was measured in the presence of an amino acid mixture and the observed values agreed with those predicted by calculation according to the technique of Read et al. (1963).