This article summarizes the published data on the intestinal microflora in breastfed infants published during the last 15 y. Enterobacteria and enterococci are found in high numbers in most infants during the first week of life. Bifidobacteria and Bacteroides spp. are found in increasing numbers at the following weeks. The intestinal microflora in breastfed infants can also be followed by different biochemical parameters. Acetic acid is found in higher concentrations in breastfed than in formula-fed infants. Degradation of mucin starts later in breastfed than in formula-fed infants. The conversion of cholesterol to coprostanol is also delayed by breastfeeding. Geographical differences in the composition of the intestinal microflora in infants have been reported, i.e. enterobacteria, enterococci, bifidobacteria, lactobacilli and bacteroides show different occurrences in developed and developing countries. There are minor differences in the infant's intestinal microflora due to breastfeeding or/and formula feeding.