Kinetics of batch cultivation of four species of Bifidobacterium in milk were examined in detail. Bifidobacteria could grow well in milk inoculated with cultures prepared in a synthetic medium. Cessation of growth occurred, however, in pH-controlled batch cultures, although incomplete utilization of lactose was observed. Lactate and acetate accumulation caused limitation on growth of bifidobacteria leading to an uncoupling of biomass and product formation. From 70 to 75% of both final lactate and acetate concentrations were produced during the stationary growth phase of Bifidobacterium bifidum, Bifidobacterium breve, and Bifidobacterium longum cultivated in milk, whereas Bifidobacterium infantis produced less acetate or lactate during this phase.