SummaryThe concentrations of iron, copper, zinc, calcium, magnesium, sodium, potassium, protein, carbohydrate, and fat were analyzed in milk from rhesus monkeys (Macaca mulatta) during the course of lactation. Concentrations of iron, copper, zinc, magnesium, sodium, potassium, and protein were higher in milk of early lactation (colostrum) than in mature milk, while concentrations of calcium increased with lactation time. Concentrations of zinc in monkey colostrum and mature milk were similar to that of human milk, while iron, copper, calcium, and protein concentrations were higher than in human milk.