Mancozeb (MCZ) is known to have detrimental effects on the reproductive system, but the toxicity of MCZ on immune responses has not been systematically investigated. We investigated the effects of MCZ exposure on the activities of murine peritoneal macrophages through evaluation of MCZ-induced alteration of nitric oxide (NO) production and tumor necrosis $factor-{alpha}(TNF-alpha)$ synthesis. Macrophages were examined ex vivo from mice orally treated with various doses of MCZ for 5 consecutive days per week for 4 weeks (subacute exposure, 250, 1000, 1500 mg/kg/day) followed by culture for 2 $(TNF-{alpha})$ or 3 days (NO) in the presence of LPS plus $IFN-{gamma}$. Macrophages from naive mice were also cultured with various concentrations of MCZ (0.05, 0.25, 0.5, 1 and 2 ${mu}g//mIL$ in the presence of LPS plus $IFN-{gamma}$ for 2 $(TNF-{alpha})$ or 3 days (NO) in vitro. NO production was decreased with the in vitro exposure to all concentrations of MCZ. However, the amount of NO production by peritoneal macrophages from MCZ-subacutely exposed mice was increased in comparision with that of control group. In vitro, MCZ suppressed $(TNF-alpha)$ secretion with significant reduction at 2 ${mu}g/mL$ MCZ. Conversely, $(TNF-{alpha})$ release was enhanced ex vivo. This study provides the substantial evidence on MCZ-induced alternation in macrophage activity. In order to clearly understand the contrasting effect of MCZ on peritoneal macrophage activity, it is necessary to further investigate the influence of major metabolite of MCZ (ETU) exposure on the NO production and $(TNF-{alpha})$ synthesis.