In vitamin A-deficient children, increased rates of bacterial infections in the intestine have been observed. The adherence of bacteria is a prerequisite for invasion. Thus, the effect of vitamin A deficiency on the adherence of fimbriated and nonfimbriated Salmonella typhimurium to isolated small intestinal enterocytes was studied. Male weanling rats matched by weight were divided into three groups: one group was fed a vitamin A-free diet for 8-12 weeks; another was given the same diet supplemented with retinol acetate; a third group matched for age served as controls. The vitamin A-deficient group showed a significantly lower growth rate and lower serum retinol levels than either the retinol acetate-supplemented or control groups. In all the groups, S. typhimurium possessing mannose-sensitive fimbriae adhered to enterocytes in significantly larger numbers than the nonfimbriated strains. The number of fimbriated S. typhimurium bound to enterocytes from the proximal small intestine was significantly higher in the vitamin A-deficient rats than in the pair-fed vitamin A-supplemented group (19.3 +/- 14.9 versus 7.8 +/- 5.0; p less than 0.05) or the control group (19.3 +/- 14.9 versus 8.7 +/- 3.5, p = 0.01). The specific activities of the enterocytes lactase, sucrase, and maltase and the protein content in the vitamin A-deficient rats were similar to those in the controls. These results demonstrate that vitamin A deficiency in rats is associated with the increased ability of S. typhimurium to adhere to proximal small intestinal enterocytes. However, the possible changes in the membrane of the enterocyte do not include decreases in brush border disaccharidases or protein content.