Two experiments were conducted using neonatal rats and lambs. The intestinal lumen of neonatal rats was infused with radiolabelled syngeneic lymphocytes, whereas the intestine of lambs was infused with radiolabelled allogeneic maternal lymphocytes. The results of both experiments indicated that radiolabelled cells were absorbed by the intestine as judged by autoradiographic studies of intestinal tissue. Furthermore, in lambs it was possible to show that these cells were transported via the lacteal lymph ducts to the mesenteric lymph nodes. These findings suggest another mechanism by which the lactating ewe may confer immunity to its suckled young.