One of the possible mechanisms that has been proposed to underlie the deleterious effects of excess aluminum on brain function is an impairment in the normal formation of the cytoskeletal network. Based on recent reports that aluminum can promote the in-vitro polymerization of purified tubulin, in the present study we characterized the effects of high dietary aluminum on in-vitro microtubule formation in brain supernatants. Mice were fed diets containing aluminum 25-1000 micrograms/g for up to 10 weeks. Tubulin polymerization in high-speed brain supernatants was not found to be affected by dietary aluminum. However, we observed that the addition of aluminum in vitro stimulated microtubule assembly in brain supernatants from mice fed control diets, as had been previously reported. Thus, impaired brain microtubule function is not an early general biochemical lesion in aluminum toxicosis.