-Strains of bifidobacteria of human origin (Bifidobacterium bifidum, B. breve, B. infantis and B. longum) were inoculated simultaneously with mixed cultures of lactococci, citratefermenting lactococci and leuconostocs to determine their impact on biochemical characteristics of fermented dairy products. Fermentations were carried out under different conditions of temperature, milk protein concentration and ratio of acidifying/aromatic lactic acid bacteria. The survival or growth of bifidobacteria during production of fermented milk was not affected by the presence of lactic starters. On the other hand, the presence of bifidobacteria during the production of fermented milk did not influence the growth of total lactococci, citrate-fermenting lactococci and leuconostocs. The variation of the milk protein content did not modify the growth of bifidobacteria and mixed-cultures of lactic starters. However, the presence of bifidobacteria changed the final characteristic of the fermented milk. Residual lactose in fermented milks containing B. breve, B. bifidum and B. infantis was lower than that found in fermented milks without bifidobacteria and those containing B. longum. The fermented milks without bifidobacteria contained less acetaldehyde than those containing bifidobacteria whereas the concentration of diacetyl was less important in the presence of bifidobacteria. However, the ethanol concentration increased when bifidobacteria were used with mixed cultures of lactococci, citrate-fermenting lactococci and leuconostocs. A temperature of 35 °C seems to be desirable because it allows the growth of bifidobacteria without affecting in a drastic way the growth and activity of leuconostocs and other lactic starters.