Summary: Electron-microscope observations have been used to follow the low-temperature dehydration of boehmite, and show that a coherent skeleton of γ-Al₂O₃ with a porous texture is produced. For material fired in air the development of a number of pore systems is described. Of these the most important, as far as the dehydration process is concerned, is a lamellar pore system parallel to (001)_γ and having a regular spacing of the order of 35–40. Å. A much faster dehydration process is induced by exposure to the electron beam and results in the formation of a more randomly oriented pore structure. The observed microstructure and the calculated internal surface area are compared with the results of previous adsorption studies.