Upon activation, the small GTPase Rho D (also designated RhoHP1 and ARHD) contributes to rearrangement of the actin cytoskeleton and cell surface and also governs endosome motility and distribution. The effects of Rho D antagonize those of its family member, Rho A, by dissasembling actin stress fibers normally enhanced by Rho A. Additionally, Rho D disengages focal adhesions, resulting in retardation of cell migration. Accordingly, transfection of a constitutively active form of Rho D (designated Rho D G26V) reverses the invasive phenotype of Galphaolf induced cells, implying the possiblity of a therapeutic use for activated Rho D in counteracting tumor metastasis.