The ability of thioglycollate-elicited peritoneal macrophages (PM) from young and senescent C57BL/6J mice to produce oxygen free radicals was assessed by luminol-dependent chemiluminescence (CL) after introduction of phagocytic stimuli. A significant age-dependent variation in the CL response was detected. A 2-fold increase in the oxygen reactive species was produced by senescent PM in response to latex and zymosan stimulation; but, the capacity to ingest latex and zymosan A particles did not vary significantly between PM from young and senescent mice. Peritoneal macrophages from both age groups responded much more vigorously to opsonized zymosan. The response of the PM from young mice was, however, 2.8-fold higher than that of old ones. There was no age-related difference in oxygen free radical production after stimulation with phorbol myristate acetate (PMA). Also, no age-dependent differences were found in the relative contribution of the various oxygen reactive species O2.-, OH., 1O2 and H2O2) to the overall oxidative burst, with latex zymosan A or PMA.