To explore possible mechanisms of the resistance of Mycobacterium avium complex (MAC) intracellular parasites to the antimicrobial activity of macrophages (MΦs), effects of the lipid components of these parasites on the MΦ respiratory burst were investigated. In this study, the MΦ respiratory burst was measured by luminoldependent chemiluminescence generated through the peroxidase-mediated halogenation reaction in murine peritoneal MΦs in response to phorbol myristate acetate (PMA) triggering. Some lipid fractions of MAC organisms including phospholipid (PL), polar mycoside, and apolar mycoside irreversibly suppressed PMA-induced chemiluminescence of MΦs. Their inhibitory activity was dosedependent, and their potency of inhibition was in the order listed above. PL potently suppressed MΦ chemiluminescence when administered to MΦs 10 s before PMA triggering. However, PL showed less efficacy in reducing MΦ chemiluminescence when added at 30 s or 80 s after PMA triggering. Moreover, when PL was administered to MΦs producing chemiluminescence in response to PMA triggering 30 s before PL addition, an approximately 1-min time lapse was observed before apparent suppression of MΦ chemiluminescence. These findings suggest that the PL-mediated suppression of MΦ chemiluminescence was due in part to inhibitory effects of PL on the PMA triggering process and process of photoemission by target MΦs.