AbstractThis study reports the modulating effect of some dairy products on initiation of putative preneoplasic lesions in rat colon (aberrant crypts) by 1,2‐dimethylhydrazine dihydrochloride. Uninoculated skim milk, skim milk fermented with Bifidobacterium sp Bio (Danone strain 173010), and a suspension of the same lactic acid bacteria were incorporated in the animals’diet. The tested diets significantly reduced the incidence of aberrant crypts compared with the control diet by 51%, 49%, and 61%, respectively.The effects of the diets on cecal pH, hepatic UDP‐glucuronyltransferase activity, and cecal microflora enzymeβ‐glucuronidase were also studied. There was no significant difference in cecal pH between rats fed experimental diets and control rat. The diet supplemented with the Bifidobacterium strain suspension significantly decreased only the cecalβ‐glucuronidase activity. Both enzyme activities were reduced in rats fed fermented skim milk‐or uninoculated skim milk‐supplemented diets compared with control animals.