An investigation of the physiological and biochemical characteristics of the Bifidobacterium bifidum no. 1, B. adolescentis MC-42, and B. adolescentis 94-BIM strains showed that bifidobacteria with a higher growth rate produced greater amounts of the end fermentation products, acetate and lactate. The growth of the strains in batch cultures was found to be inhibited by acidic fermentation products. The growth of B. bifidum no. 1 in a batch mode lasted 100 h at a population density of 10(6) CFU/ml and the growth of B. adolescentis MC-42 and 94-BIM lasted 96-120 h at population densities from 10(4) to 10(7) CFU/ml. Analysis of the bifidobacterial populations by light and electron microscopy showed that they represent conglomerates of cells with lysed cytoplasm in the cell center and intact cytoplasm in the apical parts of the cells. The maximum production of extra-cellular and cell-bound proteinases was observed in the logarithmic growth phase. By the 120th h of cultivation, the metabolic activity of cells, the production of proteinases, and the protein content of bifidobacterial cultures considerably decreased. In the first, second, and third subcultures of 96-h-old bifidobacterial cells on fresh nutrient media, the population density of bifidobacteria and their normal physiological and biochemical characteristics were restored after 48 to 72 h of cultivation.