Background:From 5 months of age, infants are progressively introduced to a variety of foods which influence the equilibrium of the intestinal microflora.Methods:Thirty-five children aged 10-18 months from 8 day care centers in France were studied. Fecal specimens were examined for their biochemical and microbiological criteria.Results:BifidobacteriaandBacteroidesbelong to the predominant populations (9.7 and 8.6 log 10 cfu/g, respectively). The mean level of enterobacteria and enterococci were 8.0 and 7.8 log 10 cfu/g, respectively. Only 10% of the infants presented a lactobacilli amount above 6 log 10 cfu/g. Most feces had similar pH values (mean 6.4), percentage of water (mean 76.4%), and short chain fatty acid, ammonia and lactic acid concentrations (means 77, 6.7 and 2.3 μmol/g, respectively). β-galactosidase had the highest activity (106 IU/g of protein) and nitroreductase, the lowest (0.1 IU/g of protein). α-glucosidase and nitrate reductase showed intermediate values of 17 and 4 IU/g of protein, respectively. With the exception of 4 infants, β-glucosidase and β-glucuronidase values were low (4 and 2 IU/g of protein). Age and day care center were not significant factors for most parameters studied, except that rotavirus was related to day care center, with detection in 5 infants from the same center.Conclusions:Many biochemical parameters were comparable to those found in adults, with the exception of ammonia concentration and β-galactosidase activity. The fecal bacterial profile was different than in adults, with moreBifidobacteriathanBacteroidesand higher levels of facultative anaerobes. One infant suffering from gastroenteritis had distinctive biochemical and bacterial parameters.