'A.B.G. is a recipient of a research grant from Fundacao de

SUMMARY In experimental animals with massive proximal intestinal resection, in vivo ileal absorp-tion of an amino acid mixture containing L-leucine and glycine as well as two different dipeptides, L-leucyl-glycine and glycyl-L-leucine, were compared. Both amino acid and dipeptide absorption were markedly enhanced in the ileal segments. However, the absorption rates from the two perfused dipeptides differed. L-leucine absorption from L-leucyl-glycine was much greater than from glycyl-L-leucine. Brush border amino-peptidase activities after resection were also increased but dissociation between absorption and hydrolytic activity occurred. This study indicates that certain dipeptides are handled differently by adapting ileal segments. Furthermore, the changes observed probably reflect mucosal cellular hyperplasia occurring in association with intestinal adaptation. Amino acids are absorbed by different transport mechanisms from the intestinal lumen depending upon whether they are present in free form or as peptides (Silk, 1974; Matthews, 1975; Matthews and Adibi, 1976). Some, but not all, amino acids are more efficiently absorbed from peptides than free amino acid mixtures (Adibi and Phillips, 1968; Craft et al., 1968; Matthews, 1977). Furthermore, peptide transport appears to be less disturbed compared with amino acid transport in some small intestinal disorders (Adibi et al., 1974; Silk et al., 1974b; Adibi, 1976). After extensive proximal resection, a profound structural and functional change occurs in residua