The purpose of this study was to determine whether there are differences in intestinal Ca and phosphate transport in mice having different peak bone densities. Intestinal transport was measured in C57BL/6 (C57) (low bone density) and C3H/He (C3H) (high bone density) female mice. Unidirectional (mucosal to serosal) transport of Ca was 58% higher in C3H compared to C57 mice, as measured by everted duodenal sacs. The capacity of the duodenal mucosa to take up Ca was also higher in the C3H mice. This uptake was highly correlated with Ca transport across the intestine. 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D), which stimulates intestinal Ca absorption, markedly stimulated unidirectional Ca transport and uptake to similar levels in both strains of mice. On the other hand, unidirectional phosphate transport in C3H mice was only 36% that of C57 mice. The mRNA levels of the plasma membrane Ca pump were 90% higher in the duodenum of the C3H mice. There was no difference between strains in duodenal calbindin or 24-hydroxylase mRNA levels. With regard to vitamin D metabolism, there was no difference in serum 1,25(OH)₂D levels or in renal 1a-hydroxylase mRNA levels. The combination of high intestinal Ca transport and low phosphate transport may contribute to the high peak bone density seen in the C3H relative to the C57 mouse.