BRMS1 (breast cancer metastasis suppressor 1) was recently identified as a novel breast cancer metastasis suppressor gene. To further characterize BRMS1-mediated metastasis suppression, we applied two-dimensional proteomic and mass spectrometry (LC-tandem MS and MALDI-TOF) analysis to identify proteins differentially expressed between highly metastatic MDA-MB-435 cells and metastasis-suppressed BRMS1-transfected MDA-MB-435 cells. Quadruplicate independent 2D gels were run and analyzed under identical conditions. Following in-gel trypsin digestion of seven differentially expressed proteins, amino acid sequence and mass profiles of the peptides were generated. Proteins were identified from the NCBI non-redundant database using the search program TurboSequest. Differential expression was confirmed for five proteins, including annexin I and alpha B-crystallin, by Northern blot analysis and immunostaining. Furthermore, we showed that both proteins were expressed in vivo in lungs containing metastasized MDA-MB-435 cells but not expressed in normal lung tissue of athymic mice. Our results suggest that annexin I and alpha B-crystallin are important cellular proteins that are down regulated through BRMS1 mediated metastasis suppression.