The capacities of bacterial DNA, extracted from Salmonella typhimurium, and lipopolysaccharide (LPS),extracted from Salmonella minnesota, to activate mouse peritoneal macrophages in vitro werecompared. Activation was assessed by estimating the levels of 3 cytokines, IL-10, IL-12, and IL-1β,at time intervals of 3, 6, 9, and 24 h after addition of LPS and/or DNA to macrophage cultures.Cytokine levels in culture supernatants were determined by enzyme-linked immunosorbentassay (ELISA) and cytokine mRNA levels were estimated based on band intensity in cultured cellsby reverse transcriptase-polymerase chain reaction (RT-PCR). Results obtained demonstrated theability of DNA and LPS to elicit increased production of all 3 cytokines as compared to controls.In the amount tested, LPS appeared to be a more potent inducer of IL-12, and IL-1β, whereasDNA induced higher levels of IL-10. DNA and LPS, used in combination, exhibited neither anadditive nor a synergistic effect. Rather, an antagonist effect appeared to occur. RT-PCR resultscorrelated well with ELISA.