While regulation of intestinal transporters is established for other nutrients, evidence concerning regulation of intestinal vitamin transport is scanty. Hence, we compared intestinal pantothenic acid (PA) uptake in mice fed diets with high, normal and deficient PA levels. PA uptake is distributed along the small intestine, Na(+)-dependent and saturable. Signs of PA deficiency were weight loss or reduced growth, then hair loss and exudation around the eyes, then diarrhea and hindleg paralysis and splenomegaly, and finally death. Treatment of mice with an antibiotic was found to be necessary to elicit severe signs of PA deficiency, probably because mice normally can obtain PA synthesized by intestinal bacteria. Dietary PA levels had no effect on intestinal PA uptake at 5 microM. A small increase in the Vmax of uptake, observed in late-stage deficiency, is probably too small to be physiologically significant. Comparison with published results for other water-soluble vitamins suggests that intestinal transporters may be regulated only for vitamins absorbed predominantly by carrier-mediated transport and subject to natural deficiency states.