The Rho family small G proteins are implicated in various cell functions, such as cell morphological change, cell motility, and cytokinesis. However, their modes of action in regulating these cell functions remain to be clarified. In the present study, we have isolated a cDNA encoding a protein which interacts with the GTP-bound form, but not with the GDP-bound form, of the Rho family members, including RhoA, Racl, and Cdc42, by the yeast two-hybrid method. This protein is kinectin, known to be a vesicle membrane anchoring protein of kinesin, which is an ATPase motor transporting vesicles along microtubules.