This work investigated the changes in the permeability of high-alumina self-flowing refractory castables based on calcium aluminate cement (CAC) and hydratable alumina binder (HAB) pretreated between 110degrees and 1650degreesC. Permeability constants k(1) and k(2) were fitted from Forchheimer's equation based on airflow tests conducted at room temperature. The results indicated that dehydration was the main contributing factor for increased permeability in bodies pretreated up to 600degreesC and that sintering effects prevailed between 900degrees and 1650degreesC. Castables based on HAB were less permeable than those based on CAC, a behavior ascribed to the type of hydrates formed and to the particle-packing features of the matrix and the matrix-aggregate interfaces.