An early event in the action of brefeldin A (BFA) is the dissociation of beta-coat protein (beta-COP) from the Golgi membrane. We have recently shown that staphylococcal ADP-ribosyltransferase (epidermal cell differentiation inhibitor (EDIN)), which specifically modifies a small G protein, rho, mimics the action of BFA and disassembles the Golgi apparatus in Vero cells (Sugai, M., Chen, C-h., and Wu, H. C. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 8903-8907). Three independent BFA-resistant cell lines (BER-40 from Vero cells, PtK1, and MDCK) showed cross-resistance to EDIN regarding the release of the beta-COP from the Golgi membrane by EDIN or BFA. BFA as well as EDIN induced disassembly of the actin microfilaments in Vero cells, and they both failed to induce the disassembly of actin microfilaments in BER-40, PtK1, and MDCK cells. BFA inhibited protein secretion in Vero cells but not in BFA-resistant cell lines, whereas EDIN did not inhibit protein secretion in either Vero or other cell lines. AlF-4 inhibited the effect of EDIN as well as that of BFA on the distribution of the beta-COP. These results suggest that an EDIN-sensitive rho protein together with trimeric and other small G protein(s) is involved in the regulation of the assembly of coated vesicles and vesicular transport in the Golgi apparatus.