The dietary bioavailable riboflavin needs for body maintenance and body protein and fat accretion were estimated in pigs. The riboflavin required to support body protein accretion was higher than that for body maintenance or fat accretion. Specifically, the riboflavin required to support protein accretion was six times higher than the riboflavin required to support fat accretion. Based on these data, both biological and environmental factors that alter body protein accretion in pigs will substantially alter riboflavin needs. In addition, the dietary bioavailable riboflavin required by high-lean, high-health pigs is greater than the current NRC (4) estimate.