Tubulin, the main component of microtubules, is a major target for antitumor drugs such as vinblastine. We have recently discovered that the betaII isotype of tubulin is present in the nuclei of cultured rat kidney mesangial cells, smooth-muscle-like cells present in the renal glomerular mesangium (Walss C, Kreisberg JI, Ludueña RF: Cell Motil Cytoskeleton 42: 274-284, 1999). Here, we have investigated the effect of vinblastine on nuclear betaII-tubulin in these cells. We have found that, at concentrations of 15 nM and higher, vinblastine caused a reversible loss of betaII-tubulin from the nucleus. Our results raise the possibility that nuclear betaII-tubulin constitutes a population of tubulin that could be a novel target for antitumor drugs such as vinblastine.