An attempt was made to isolate human strains of Bifidobacteria, all together 36, from fecal samples of 15 breast-fed infants ages 1-6 mo. These isolates were checked for their ability to grow in the presence of 1-3% bile, 0.2-0.4% phenol, and low pH (3.0-5.0) in vitro, to evaluate their capacity to grow under hostile and unfavorable conditions of the human digestive tract. Because milk is to be used as a carrier medium, their ability to grow in 10% sterile skim milk was also evaluated. The bifidobacteria count of the cultured milk samples (0, 24, and 48 h) was taken on tryptone yeast extract agar after 48 h of incubation in the presence of 10% CO2 at 37degreesC. The changes in pH and developed titratable acidity were also recorded up to 96 h of incubation. The results indicated that all the isolates obtained had reasonable resistance to pH, bile, and phenol and were capable of growing well in milk. Among the 36 isolates, Bifidobacterium bifidum (isolates no. 4, 8, and 17) and B. breve (isolates no. 25 and 26) were the most tolerant to unfavorable conditions, and they may therefore be recommended for use in fermented milk or baby food formulations as probiotic dietary adjuncts.