Lead (Pb) may affect humoral and cellular immunity, acting on lymphocytes as well as on granulocytes and monocytes. Cytokines and nitric oxide (NO) play a central role in the immune balance. In this study, plasma levels of nitrites and nitrates (NOx), IL2, IL4, IL6, IL10, TNF-α and INF-γ, were measured in healthy workers with very low (Pb-B =3.2 -18.0 μg/dL) and low (Pb-B = 9.1 -46.0 μg/dL) Pb-exposure compared to non-exposed workers. Low Pb-exposed workers (Pb-B =9.1 -46.0 μg/ dL) were found to have significantly higher plasma IL-10 levels, and tendentially higher plasma TNF-α levels compared to non-exposed workers. This is the first report of a significant increase of plasma IL-10 levels in Pb-exposed workers. Plasma IL-10 increase was influenced by blood Pb levels even after correction for main confounding factors. No difference was found in plasma NOx levels between Pb-exposed and non-exposed workers, which is in agreement with previous findings exclusively regarding groups in the general population. Low Pb-exposure can induce an increase of pro-inflammatory cytokines, such as TNF-α, with a consequent increase of other cytokines, such as IL-10, considered a T cell cross-regulatory factor, suggesting possible interference of Pb in the system of immunophlogosis. Human & Experimental Toxicology (2007) 26, 551 - 556