Mancozeb (MCZ), a polymeric complex of zinr and manganese salts of ethylene bisthiocarbamate, is widely used in agriculture as fungicidel, insecticides, and herbicides. MCZ can be occupationally and environmentally exposed to human and has been reported 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 splenocytes through evaluation of splenocytes cellularity and INF-$gamma$ synthesis. Splenocytes were examned ex vivo from mice orally treated with various doEes of MCZ for 1 day (acute exposure, 2,100, 5,000, 10,000 mg/kg) or ior 5 consecutive days per week for 4 weeks (subacute exposure,250, 1,000, 1,500 mg/kg/day) fellowed by culture for 2 days in the presence of Con A or PHA plus IL-2. Splenocytes Iron naive mice were cultured with various concentration of MCZ (50, 500, 1,000 ng/ml) in the presence of Con A or PHA plus IL-2 for 2 days in vitro. IFN-$gamma$ production was decreased with the in vitro exposure to all concentration of MCZ. The spleen cellularity and IFN -$gamma$ production by splenocytes from MCZ -acutely and - subacutely exposured mice were decreased in comparision with that oi control group.