Background: Estimation of nitrate and nitrite concentrations of milk sources may provide insight into potential health risks and benefits of these food sources for infants, children, and adults. The World Health Organization and American Academy of Pediatrics recommends exclusive consumption of human milk for the first 6 months of life. Human milk is known to confer significant nutritional and immunological benefits for the infant. Consumption of formula, cow's, and soy milk may be used as alternatives to human milk for infants. Methods: We sought to estimate potential exposure to nitrate and nitrite in human, formula, bovine, and soy milk to inform total dietary exposure estimates and recommendations. Using sensitive quantitative methodologies, nitrite and nitrate were analyzed in different samples of milk. Results: Human milk concentrations of colostrum (expressed days 1-3 postpartum; n ¼ 12), transition milk (expressed days 3-7 postpartum; n ¼ 17), and mature milk (expressed >7 days postpartum; n ¼ 50) were 0.08 mg/100 mL nitrite and 0.19 mg/100 mL nitrate, 0.001 mg/100 mL nitrite and 0.52 mg/100 mL nitrate, and 0.001 mg/100 mL nitrite and 0.3 mg/100 mL nitrate, respectively, revealing that the absolute amounts of these anions change as the composition of milk changes. When expressed as a percentage of the World Health Organization's Acceptable Daily Intake limits, Silk Ò Soy Vanilla (WhiteWave Foods, Broomfield, CO) intake could result in high nitrate intakes (104% of this standard), while intake of Bright Beginnings Soy Pediatric