An alkali-insoluble glucan synthesized from UDP-d-glucose by the particulate enzyme system from Phaseolus aureus is hydrolyzed by a highly purified exo-beta-(1 --> 3)-d-glucanase to d-glucose, to the extent of 91% in 24 hr. The alkali-insoluble glucan from GDP-d-glucose formed by the particulate enzyme system from the same plant which is known to be (from chemical data) a beta-(1 --> 4)-d-glucan (cellulose) is not acted upon by this glucanase.