The active oxygen produced from stimulated phagocytic cells emits luminol-dependent chemiluminescence (CL) upon reaction with luminol. So the active oxygen was measured by using the CL and the results of this were compared with those by the LDH-NADH method. Moreover, effects of nonsteroidal anti-inflammatory drugs (NSAID) on the generation of active oxygen were studied by both methods. Rat peritoneal and pleural exudated cells (PEEC and PLEC) emitted strong CL on incubation with zymosan, but that from rat whole blood cells was very weak. The effects of superoxide dismutase, catalase, NaN3 and L-ascorbic acid on the generation of active oxygen from rat phagocytic cells were different between CL and LDH-NADH methods. These discrepancies seem to be due to the different kinds of active oxygen that can be measured by both methods. Except for BW-755C, most of the NSAID had only a slight inhibitory effect on the generation of active oxygen measured by both methods, and the ex vivo effect was the same as that observed in vitro. It may be considered that NSAID decrease the phagocytic function of cells by non-specifically stabilizing the biological membrane and inhibit slightly the generation of active oxygen from phagocytes. On the other hand, the CL method could be performed not only in PEEC and PLEC, but also in whole blood cells. From these results, it was suggested that CL measurement can be used as a simple and valuable method for the detection of all types of active oxygen including superoxide anion radical and its metabolites and for testing cellular functions and drug actions on them.