The treatment of timothy grass stem tissue with sodium hydroxide in the presence of air resulted in a rapid fall in the amount of soluble D-glucose and D-fructose in the plant material. Lactic acid and other degradation products with retention times on gas-liquid chromatography similar to saccharinic acids were formed. The calcium salt of cc-~-g~ucoisosacchar~n~c acid, although taken up by the rclmen bacteria and holotrich protozoa studied, was not readily metabolised as assessed by gas, volatile fatty acid and lactate production and incorporation studies. Using the same criteria, the calcium salts of a,p-D-glucometasaccharinic acids were not assimilated by either of the microbial cell preparations isolated from sheep receiving a diet of hay and sugar-beet pulp. The uptake of D-glucose by the bacterial and protozoal preparations was affected in incubations in vitro containing increased concentrations of the a-D-isosaccharinic acid and D,L-lactic acid, respectively.