Diets prevalent in vegetarian populations using rice and other whole grains as staples with little consumption of yellow vegetables are low in riboflavin. These diets have poor bioavailability of iron and zinc because metals are present as inorganic salts with low solubility. Riboflavin has the capacity to form complexes, and supplementation of riboflavin may result in increased absorption of zinc and iron, thus increasing the cellular transport. Therefore, riboflavin may have direct as well as indirect effects on growth. Using this as the conceptual basis, experiments were conducted on pregnant and lactating mice. Two groups, each of 12 mice (9 females and 3 males), were observed on a low-riboflavin rice-based diet (adequate in all other nutrients), one with and one without supplementation of 10 mg riboflavin/kg diet. There was significant improvement in the growth parameters like percent conception, mean weight gain in pregnancy, mean weight of pups at the age of 21 d, and percentage hemoglobin due to riboflavin supplementation (p < 0.05). Percent zinc absorption, for the low-riboflavin diet, the supplemented diet, and the synthetic control diet were 16.4+/-5.7, 33.7+/-8.9, and 44.6+/-4.0, respectively, indicating the beneficial effect of riboflavin supplementation on iron and zinc utilization.