AbstractThe in vitro effects of aneuploidogens on taxolpurified microtubules from whole Drosophila melanogaster and mouse brain were studied by a spectrophotometric assay and electron microscopy. Colchicine, acetonitrile, propionitrile, acrylonitrile, dimethylsulfoxide (DMSO), griseofulvin, and cadmium chloride inhibit microtubule assembly, whereas methoxyethyl acetate (MEA) does not. Qualitatively similar results were observed with D. melanogoster and mouse brain microtubules. The in vitro results from D. melanogaster correlate well with previously published results from in vivo assays monitoring induced sex chromosome aneuploidy in that effective aneuploidogens are observed to affect microtubule assembly. The inclusion of taxol does not appear to qualitatively affect the assembly assays with the chemicals tested. In contrast with results from assembly assays, the tested aneuploidogens, including colchicine, do not promote disassembly to taxol‐purified microtubules. It is possible that taxol has shifted the equilibrium and stabilized the formed microtubules to the extent that they are no longer sensitive to aneuploidogen‐induced disassembly.