Abstract: The invention relates to an infant formula comprising a source of protein in an amount of not more than 2.0 g/100 kcal, a source of lipids, a source of carbohydrate and a probiotic wherein the probiotic is present in an amount equivalent to between 102 and 105 cfu/g of dry formula. The invention further extends to the use of such an infant formula to modulate the immune system of a neonatal infant to promote the development in the first few weeks of the life of the infant of a beneficial intestinal microbiota comparable with that found in breast fed babies as well as to promote the maturation of the immune system of a neonatal infant in the first few weeks of life.