The adherence of radiolabeled fimbriated (S 7471 ØF) and nonfimbriated (S 7471 N)Salmonella typhimuriumto small intestinal rat enterocytes was examined during postnatal development. The fimbriated strain invariably adhered in higher numbers than the nonfimbriated strain during all periods of development. The capability of enterocytes to bind Salmonella increased significantly during postnatal development and reached adult levels at weaning time (21 days of age). Bacterial adherence to enterocytes was similar if the cells were isolated from the proximal or the distal small intestine. Early weaning of pups did not affect the capability of enterocytes to bind Salmonella. Pretreatment of isolated enterocytes from adult animals with rat's milk before exposure to Salmonella had no effect on the level of bacteria that adhered per enterocyte. Conversely, pretreatment of Salmonella with rats' milk before binding to enterocytes from adult animals also did not alter the level of bacteria adhered per enterocyte. These results suggest an age-dependent, postnatal development of available receptors forS. typhimuriumon rat enterocytes. The acquisition of these receptors is not affected by mother's milk and is unaltered by early weaning. (Pediatr Res24: 508–511, 1988)