Colonic fermentation plays an important role inthe prevention of lactose intolerance and intestinaldisorders. The objectives of this study were to evaluatewhether supplementation with bifidobacteria modify colonic fermentation of lactose andshort-chain fatty acid production and to assessinfluence of the pH in an in vitro continuous culturesystem. There was a significantly greater reduction inlactose concentrations at pH 6.7 than that at either pH6.2 or pH 5.7, accompanied by the highest-galactosidase activity and D-lactate production.Bifidus supplementation reduced lactose and D-lactateconcentrations and increased acetate production at pH 6.7. Thestudy demonstrates that lactose is rapidly metabolizedby colonic bacteria and lactose fermentation in vitro ispH dependent with a maximum rate at pH 6.7. Bifidobacteria supplementation may have thepotential to improve lactose fermentation and tomanipulate SCFA and lactate production.