Cyclooxygenase (COX)-2 inhibitors that belong to non-steroid anti-inflammatory drug family have been shown to have an apoptosis-inducing effect on neoplastic cells. In the present study the effect of nimesulide (NIM), a specific COX-2 inhibitor, on apoptosis and interactions between BCL-2 family death promoters BAX and BID and BAX and VDAC-1 were examined in human colon adenocarcinoma COLO 205 cells. Laser scanning cytometry was applied for the measurement of expression and aggregation of apoptosis-related proteins and quantitative analysis of NIM-induced apoptosis. Double-staining immunoconfocal and immunoelectron microscopy were used for subcellular colocalization of examined proteins. NIM induced apoptosis of COLO 205 cells in a dose-dependent manner. This was accompanied by: (1) a decrease in intracellular prostaglandin (PG) E2content; (2) subcellular redistribution and aggregation of BAX and BID on organellar membranes and within the nucleus; (3) colocalization of BAX with BID and BAX with VDAC-1 on organelles; and (4) survival of cells with the highest BCL-2 aggregation. A similar pattern of subcellular redistribution and colocalization of BAX with BID and BAX with VDAC-1 suggests that BAX (in association with BID) controls the function of VDAC-1 and its permeability for apoptogenic factors released from mitochondria of COLO 205 cells stimulated to apoptosis with NIM.