The transport of glycylsarcosine (Gly-Sar) has been investigated in cells isolated from the proximal cecum and rectum of the chick, and their characteristics have been compared with those of the jejunal dipeptide transport system. Results show that 1) cecal and rectal cells are capable of actively accumulating Gly-Sar. 2) Gly-Sar initial uptake and steady-state accumulation in cecal and rectal cells were decreased in Na(+)-free mannitol-substituted medium. However, in both cell types, as in jejunal cells, intracellular accumulations higher than one can be observed in the absence of Na+. 3) By lowering the medium pH from 7.4 to 6.0, the Gly-Sar accumulation was stimulated in both cecal and rectal cells. 4) Addition of 1 mM amiloride inhibited Gly-Sar uptake by the cecal and rectal cells. We conclude that proximal cecum and rectum have a dipeptide transport system with properties similar to those found in the jejunum.