Whole, moist barley treated with ammonia (A), whole, untreated barley (WU) and ground barley (G) were fed with hay and a little high protein, mixed concentrate. Digestibilities of dry matter, organic matter and crude fibre, assessed with young adult female sheep, were highest in diet A and lowest in diet G. The digestibilities of dry matter and crude fibre were also higher in diet WU than in diet G. Digestibility coefficients for dry matter and organic matter in barley, calculated by difference, appeared higher in A and in WU than in G. Young female sheep fed on the above diets from the age of 7 to 11 months ate more hay and gained more weight on A than on G; again diet WU was intermediate. Differences also occurred between the three groups as regards volatile fatty acids in the rumen fluid. Sheep on A or WU had a higher pH in the rumen fluid than those on G. Finally, sheep on A gave birth to more offspring than those on WU or G. All these differences were significant.