The effects of consuming zinc-fortified ready-to-eat breakfast cereals were determined in a double-blind controlled study. The 96 healthy young children who participated (mean age 58 months) consumed either zinc-fortified cereal, providing 25% United States Recommended Dietary Allowance per 1 ounce serving (test children) or nonzinc-fortified cereals (controls) for a 9-month period. The test children were calculated on average to receive an additional 2.57 mg of zinc per day from this fortification program. This increment increased their mean daily zinc intake to a level that approached the Recommended Dietary Allowance (10 mg) of the National Academy of Sciences for children less than 10 years of age. By the end of the period, the test children (combined sexes) had a mean increment of plasma zinc that was 6.5 micrograms/dl greater than that of the control children (P less than 0.02). The test girls had a greater increment (28.5 micrograms/g) in hair zinc content than controls girls (P less than 0.05). There were no significant differences in other biochemical parameters including plasma copper and serum cholesterol. No significant differences in food intake or growth velocity were associated with the consumption of the zinc-fortified cereal. Multiple sex and time related differences occurred in plasma, hair, urine, and parotid saliva zinc concentrations that were unrelated to the type of cereal consumed.