Direct demonstrations implicating the microtubule cytoskeleton in insulin-mediated GLUT4 translocation are beginning to emerge, and one role of the microtubule network appears to be the provision of a solid support for GLUT4 vesicle movement. In the current study we show that insulin treatment increases total polymerized -tubulin in microtubules in a time and dose dependent manner that coincides with established insulin-mediated changes in GLUT4 translocation. Insulin stimulated growth of microtubules through a pathway that requires tyrosine kinase activity, as indicated by inhibition of the effect after treatment with genistein. Insulin-mediated growth was not inhibited by treatment with the MEK inhibitor, PD98059 or by wortmannin, indicating that the effect does not require activation of ERK 1/2 or PI 3-kinase. Depolymerization of the actin cytoskeleton with latrunculin B abrogated the effect of insulin on microtubule polymerization, indicating that an intact actin network is a requirement for insulin-dependent modulation of microtubules. Using methods that measure insulin-dependent GLUT4 translocation in populations of adipocytes as opposed to individual cells, we show a statistically significant reduction in translocation (30% inhibition) in the presence of low concentrations of nocodazole (2 µM). This concentration incompletely depolymerizes the microtubule network, revealing that partial depolymerization of microtubules is sufficient to inhibit GLUT4 translocation. It is likely that stabilization of the microtubule network contributes to insulin stimulation of GLUT4 translocation.