Objective: To assess the effects of the ingestion of milk, yoghurt (10 8 bacteriaaml), heat-treated yoghurt (`15 bacteriaaml) and two products obtained by dilution of yoghurt with heat-treated product (10 6 and 10 5 bacteriaaml) on hydrogen production and symptoms of lactose intolerance in lactose malabsorbers. Design: Double-blind, randomised cross-over design. Setting: The study was performed in the phase 1 clinical unit of OPTIMED, Nancy, France. Subjects: Twenty-four male lactose malabsorbers were selected for the study. Interventions: Hydrogen production and adverse events were followed during 8 h after ingestion of the products. Results:The results clearly demonstrate that ingestion of yoghurt with 10 8 bacteriaaml leads to lower H 2 excretion and complaints than the other products. Results observed with the products containing a reduced population of livē ora remain better than those observed with milk. Conclusions: The importance of a high population of the live¯ora is underlined. Sponsorship: This work was supported by the`Mission Scienti®que de SYNDIFRAIS'.

No abstract