Rho-GDIalpha is an inhibitor of Rho-GTPases, which is involved in cancer progression. Little is known about its role in breast cancer progression. There is evidence, that Rho-GDIalpha may modulate drug resistance of breast cancer cells. To assess the importance of Rho-GDIalpha as a risk factor in invasive ductal breast cancer, cancer specimens of three groups of patients were analyzed for Rho-GDIalpha RNA (group 1, N=72 and group 2, N=73) or protein expression (group 3, N=90). In group 1, patients did not receive any adjuvant treatment, whereas, in groups 2 and 3, patients were treated with anti-estrogens and/or with chemotherapeutical drugs. Rho-GDIalpha RNA levels, measured by RT-PCR from fresh-frozen material, did not correlate with relapse-free survival in Kaplan-Meier analysis, except in a subgroup of CMF-only treated patients. In this subgroup, higher Rho-GDIalpha RNA levels were significantly associated with more favorable prognosis. Immunohistochemical analysis (group 3) confirmed the link between higher Rho-GDIalpha expression and better outcome. This was again particularly true for the CMF-only treated patients. Cox regression analysis revealed that high Rho-GDIalpha protein expression reduced the risk for a relapse by approximately 3-fold, even if adjusted for grading, tumor size, nodal and estrogen receptor (ER) status. The data suggest that Rho-GDIalpha is beneficial to patients who received adjuvant chemotherapy. Rho-GDIalpha is possibly a useful biomarker to predict the response of breast cancer patients to CMF treatment.