Different inert markers have been employed in nutritional studies, (Kotb and Luckey, 1972). The most commonly found marker in studies involving pigs is chromic oxide (Low, 1982) although it is now apparent that many problems are associated with its use. Other metal oxides, particularly titanium dioxide, may prove to be superior alternatives but further validation of their use as markers is required, (Kotb and Luckey, 1972). In an evaluation of inert markers, (Jagger et al. 1992) it was found that, for the determination of ileal and faecal apparent digestibility values in the pig, titanium dioxide at a rate of lg/kg feed was the most suitable of those tested. However, this conclusion was drawn from results obtained from one dietary treatment only. A crucial assumption of the use of inert markers is that they move in phase with the digesta which might not be the case if components vary widely in physical characteristics, leading possibly to differential adsorption of marker. Accordingly the objective of the current experiment was an evaluation of titanium dioxide in diets representing likely extremes of levels of fat or fibrous raw materials.