The intestinal microflora of 1-y-old healthy Estonian (n= 27) and Swedish infants (n= 29) was studied by quantitative culture of faecal samples. The major differences were high counts of lactobacilli and eubacteria in the former and increased numbers of Clostridia in the latter babies. Bifidobacteria and anaerobic cocci prevailed equally in both groups, while eubacteria and enterococci were the major microorganisms in many Estonian infants and bacteroides and Clostridia in many Swedish infants. The microflora of the Estonian infants was in many aspects similar to the flora prevailing in infants of western Europe in the 1960s. The results suggest a shift in the intestinal microflora among infants in western industrialized countries.