This multicentric, randomized, double-blind and controlled study aims to examine the effect of a fermented dairy product containing the probiotic Lactobacillus casei DN-114 001 (Actimel® = tested product) on the incidence of respiratory and gastro-intestinal common infectious diseases (cumulated number of infections during the intervention period: primary criteria) in children aged 3-6 years, attending day care centers.Volunteers received either 200g/day of tested product (N=300) or control product (N=299) for 3-months, followed by a 1-month follow-up.