Intestinal microflora in 17 breast-fed(BF) and 14 formula-fed (FF) newborn infants at about 1 week after birth were investigated to determine the floral differences of the two lactation groups. The fecal conditions were significantly different between the two groups in that the number of subjects who showed watery feces, and the times of defecation per day, were higher in the BF group. In addition, the mean fecal PH of the BF group was lower than that of the FF group. The dominant species in the BF groups which showed the highest count among the species of microflora was bifidobacteria , while the dominant species in the FF group was streptococci. The frequency of staphylococci and the count of bifidobacteria were significantly higher in the BF group. However, the frquencies of streptococci and Peptococcaceae were higher in the FF group. Through the differences were not significant, the frequency of bvifidobacteria and the count of staphylococci were higher in BF group, whereas the frequencies of bacteriodes, clostridia, enterobacter and the count of clostridia were higher in FF group.