The paper reports the development of three dimensional (3-D) silicon microstructures and the utilization of these microenvironments for discriminating between normal fibroblast (HS68) and breast cancer cells (MDA-MB-231). These devices consist of arrays of microchambers connected with channels and were fabricated using a single-mask, single-isotropic-etch process. The behavior and response of normal fibroblast and breast cancer cells, two key cell types in human breast tumor microenvironments, were explored in terms of adhesion and growth in these artificial 3-D microenvironments having curved sidewalls. Breast cancer cells formed stable adhesions with the curved sidewalls however fibroblasts stretched and elongated their cytoskeleton and actin filaments inside the microchambers. Statistical analysis revealed that fibroblast cells grew on both flat silicon surfaces and inside the microchambers regardless of microchamber depth. However, the localization of breast cancer cells in these same substrates was dependent on the microchamber depth. After 72 h in culture, the ratio of the number of breast cancer cells on flat surfaces compared to breast cancer cells inside the microchambers was significantly decreased within the deeper microchambers; for microchambers having depths 88 mum less than 5% of the breast cancer cells grew on the flat surfaces. This behavior was sustained for 120 h, the longest time point examined. The results suggest that certain 3-D silicon microstructures have potential application as a tool to detect breast cancer cells and also as a platform for separating normal fibroblasts from breast cancer cells for cancer diagnosis applications.