The digestibility of alkali treated ripe hulls(0, 2.5, 5, 10 and 15% NaOH/100g rice hull dry matter)+lucerne pellet(50 : 50) and lucerne pellet (100%) were examined to sheep. Metabolism studies confirmed the pattern of intake of alkali treated feed established in the feeding trial and showed there to be no difference in level of intake of the 5.0% alkali treated pellet diet compared with a diet of pellets composed solely lucerne. The apparent digestibility of the following feed fractions: organic matter, cell wall constituent day matter, cell constituents organic matter, acid detergent fibre were all significantly (P$lt;0.05) increased only for the lob alkali treated feed when compared with the control. No significant differences in digestibility values obtained between diets of 2.5, 5, 10 and 15% alkali. Studies on diets comprised solely of the lucerne as used in the mixed roughage feeds allowed partition of apparent digestion of the rice hull component. For rice hull OM, CWC DM, the 15% level of alkali treatment led to a significantly greater percentage disappearance of matter when compared to control rice hull material. In terms of the amounts of these fractions digested both the 15% and 5% alkali treated feeds were significantly (p$lt;0.05) greater than 0% alkali feed. For example, the basic unit of rice hull roughage (cell wall organic matter content) was digested to an extent of 61.5% whereas control material was digested to an extent of 12.9% leading to significant differences in daily intake of digestible organic matter derived from rice hull cell wall material.