Lactose maldigestion and intolerance affect a large part of the world population. The underlying factors of lactose intolerance are not fully understood. In this review, the role of colonic metabolism is discussed, i.e. fermentation of lactose by the colonic microbiota, colonic processing of the fermentation metabolites and how these processes would play a role in the pathophysiology of lactose intolerance. We suggest that the balance between the removal and production rate of osmotic-active components (lactose, and intermediate metabolites, e.g. lactate, succinate, etc.) in the colon is a key factor in the development of symptoms. The involvement of the colon may provide the basis for designing new targeted strategies for dietary and clinical management of lactose intolerance. © 2008 The Authors. Chemicals / CAS: lactic acid, 113-21-3, 50-21-5; lactose, 10039-26-6, 16984-38-6, 63-42-3, 64044-51-5; succinic acid, 110-15-6; Lactates; Lactose, 63-42-3