Background: The Ras and Rho family of GTPases serve as essential molecular switches in the downstream signalling of many cytokines involved in the regulation of renal fibroblast activity. Prenylation is a post-translational process critical to the membrane localization and function of these GTPases. We studied the effects of a farnesyltransferase inhibitor BMS-191563 and geranylgeranyltransferase inhibitor GGTI-298 on renal fibrogenesis in vitro. Methods: Functional studies examined the effects of BMS-191563 and GGTI-298 on rat renal fibroblast kinetics, collagen synthesis and collagen gel contraction. Pro-collagen α1(I) mRNA expression was measured by Northern analysis and CTGF expression by Western blotting. Results: Fibroblast proliferation was significantly reduced by both agents. Exposure of fibroblasts to BMS-191563 resulted in a significant reduction in total collagen production and pro-collagen α1(I) mRNA expression, an effect also observed but to a lesser degree with GGTI-298. Both agents significantly reduced CTGF protein expression. Fibroblast-mediated collagen I lattice contraction was decreased at 48 h by GGTI-298, an effect not observed with BMS-191563. Consistent with this finding, marked actin filament disassembly was evident by phalloidin staining of fibroblasts exposed to GGTI-298. Conclusion: BMS-191563 and GGTI-298 exhibit different effects on renal fibroblast function reflecting their predominant roles in inhibiting prenylation of Ras or Rho proteins respectively. Further studies are warranted to establish their potential therapeutic application in the treatment of progressive renal disease.