In this study, we investigated the role of Ca(2+) in curcumin-induced paraptosis, a cell death mode that is accompanied by dilation of mitochondria and the endoplasmic reticulum (ER). Curcumin induced mitochondrial Ca(2+) overload selectively in the malignant breast cancer cells, but not in the normal breast cell, contributing to the dilation of mitochondria/ER and subsequent paraptotic cell death. In addition, we found that simultaneous inhibition of the mitochondrial Na(+)/Ca(2+) exchanger (mNCX) and proteasomes can trigger a sustained mitochondrial Ca(2+) overload and effectively induce paraptosis in malignant breast cancer cells.