Macrophage respiratory burst, as assessed by H2O2 and O2- production, and HMS and chemiluminescence activity was investigated in a variety of conditions in macrophages from Bcg-congenic mice. Measurement of HMS and chemiluminescence in splenic macrophages challenged in vitro with BCG showed that the Bcgr cells were more stimulated by the challenge than their Bcgs counterparts. H2O2 production was measured in Bcgr and Bcgs splenic macrophages. PMA-triggering and LK-triggering were shown to stimulate a similar degree of H2O2 production Bcgr and Bcgs macrophages. In contrast, in vitro phagocytosis of BCG was shown to trigger superior production of H2O2 and O2- in the Bcgr splenic macrophages as compared to their Bcgs congenics. Finally, following the in vivo infection with BCG Montreal, Bcgr splenic macrophages were superior producers of H2O2 (both spontaneous and PMA-triggered) in the early phase of infection.