Peritoneal macrophages from the house mouse (Mus musculus) were exposed to variable lead (Pb) concentrations (0.2, 2, 20 and 40 microM) to better understand lead cytotoxicity and its damage to the immune response. Phagocytes were exposed to 20 and 40 microM Pb for 72 h, and macrophages were exposed at lower concentrations (0.2, 2 and 20 microM Pb) for 24h and 72 h. Dysfunctions in macrophage immune activity were examined by measuring phagocytic activity, nitric oxide production, endosomal/lysosomal stability and cell adhesion. Lead affected all macrophage functions, even at low concentrations, by reducing the phagocytic index, nitric oxide production, endosomal/lysosomal system stability and cell adhesion, and upregulating the antioxidant enzymatic activity of catalase. We demonstrate that lead affects the redox status of the cells and suggest that the immunomodulatory effects at low dosages on mouse macrophages reduces their ability to protect the host against infectious agents.