The ability of many microtubule-targeting agents to induce mitotic block has been known for years and has been taken advantage of both in basic research, as well as in clinical settings in the treatment of cancer, diabetes, and a variety of other human diseases. However, the molecular details surrounding structural changes of microtubules in the presence of microtubule-targeting agents still evade us. Improving our understanding of said details will enable pharmacologists of the future to develop more targeted, specific therapeutics to aid patients suffering from a plethora of disease. In this study, we used an antibody-based approach to shine light on in vivo microtubule structural alterations that occur in conjunction with the treatment of mammalian cells with vinca alkaloid drugs. COS7 cells were exposed to vinblastine or vincristine for 12 hours, then permeabilized, fixed, and stained with several antibodies before being examined under a confocal microscope. We then employed a humanized-antibody, hMB11, which recognizes the structural conformation of GTP-bound tubulin, in an effort to visualize hMB11 staining along astral microtubules during metaphase and to quantify the difference in hMB11 staining in the presence and absence of vinca alkaloid drugs. These data indicate a statistically significant increase in the localization of hMB11 to astral microtubules in COS7 cells arrested in mitosis in a metaphase-like state with nanomolar concentrations of vinblastine and vincristine as compared to their control counterparts. Nanomolar concentrations of microtubule-targeting drugs have been shown to suppress the growing and shortening of microtubules in living cells. These changes in the behavior of microtubules are associated with incomplete congression of chromosomes to the metaphase plate. Our findings suggest that drug-induced changes in the structure of microtubules may underlie alterations of microtubule and chromosome dynamics.