Exogenous xylanases reduce anti-nutritional factors in feedstuffs and help optimise digestion in the small intestine through their positive effects on water holding capacity, nutrient packaging, digesta viscosity and flow. The net effect is reduced likelihood of both undesirable bacterial proliferation in the small intestine and migration of bacteria from the large to the small intestine leading to a disease challenge and hence reduced performance. Osmotic upsets have also been observed with pigs fed cereal-based diets, and the osmoregulatory role of betaine may strengthen the pig’s defence of this condition. As the mode of action of betaine is different from enzymes, it has been postulated that piglets may be responsive to combinations of these additives. The object of the experiment reported was to study the performance of weaner pigs fed diets containing differing rates of inclusion of exogenous xylanase and betaine.