The toxic syndrome resulting from in vivo exposure to n-hexane or n-hexane derivatives may, in part, be a manifestation of altered tubulin and microtubule properties. The effect of in vitro gamma-diketone derivatization was first studied using purified bovine brain tubulin and the results were then verified in tubulins purified from target organs of an experimental species. Microtubule assembly and structure were modified after in vitro incubation with 2,5-hexanedione (2,5-HD) as follows: 2,5-HD derivatization of purified tubulin resulted in an alteration in microtubule assembly kinetics, most prominently a decrease in the length of the nucleation phase, the alteration in assembly kinetics was accompanied by the formation of a covalently crosslinked tubulin dimer, mixing experiments which combined different proportions of control and treated tubulin showed that only a small amount of derivatized tubulin need be present to induce altered assembly properties, and as a result of the more rapid nucleation phase, a greater number of nucleating seeds produced more numerous and shorter assembled polymers. In vitro incubation with the 2,5-HD congener 3,4-dimethyl-2,5-hexanedione produced similar alterations in microtubule assembly. Thus, both the kinetics of tubulin polymerization and the morphology of the final assembly product were modified by in vitro gamma-diketone incubation.