Insulin regulates metabolism through homologous receptor tyrosine kinases, and plays a role in proliferation of breast cancer cells. Our research studied whether insulin, administered separately or in combination with paclitaxel, interferes with paclitaxel-mediated biological activity in human breast cancer cells. Not only did insulin influence paclitaxel-mediated cell microtubule reorganization, but it also influenced MCF-7 cell sensitivity to paclitaxel. Furthermore, combined administrations of insulin and paclitaxel affected MAPK pathway, Raf-1 activation and p53 expression levels. Our findings indicate that insulin seems to modulate MCF-7 cell response to paclitaxel; consequently, elevated levels of insulin could influence tumor cell resistance.