Maternal food consumption, maternal body weight loss, and pup growth were studied in the following six groups of rats: vitamin D-deficient, vitamin D3-replete, vitamin D3-replete but pair-fed with the vitamin D-deficient rats and rats given either 50, 150, or 450 pmol/day of 1,25-dihydroxyvitamin D3 as their sole source of vitamin D by continuous infusion from an Alzet osmotic minipump. As expected, vitamin D-deficient rats were hypocalcemic and lost body weight, and their pups stopped growing at 1 wk of age. Food consumption by the vitamin D-deficient rats was one-third that of the vitamin D3-replete rats. Although normalization of plasma calcium levels was not perfect, 1,25-dihydroxyvitamin D3 treatment led to normal maternal food consumption, prevented maternal body weight loss, and promoted normal pup growth. Pups from the vitamin D3-replete rats pair-fed with the vitamin D-deficient rats did not grow properly and their dams lost body weight. These data indicate that 1,25-dihydroxyvitamin D3 is fully capable of replacing vitamin D3 in promoting maternal food consumption in lactating rats and that maintaining adequate food consumption is a major factor in the stimulatory effect of vitamin D3 on pup growth and hence milk production. The anorexia and reduced milk production of vitamin D-deficient lactating rats did not result from changes in plasma glucose or triglyceride levels.