Rab10, a mammalian homolog of the yeast Sec4p protein, has previously been associated with endocytic recycling and biosynthetic membrane transport in cultured epithelia and with Glut4 translocation in adipocytes. Here, we report that Rab10 associates with primary cilia in renal epithelia in culture and in vivo. In addition, we find that Rab10 also colocalizes with exocyst proteins at the base of nascent cilia, and physically interacts with the exocyst complex, as detected with anti-Sec8 antibodies. These data suggest that membrane transport to the primary cilum may be mediated by interactions between Rab10 and an exocyst complex located at the cilium base.