Abstract The tuberculosis infection triggers in the host a complex immune response and the involvement of CD4+ lymphocytes and interferon-gamma (INF-γ) in the control processes has been reported. Since nutritional status, e.g. regarding zinc may have potent effects on the immune response, we conducted a zinc supplementation study to gain more knowledge on its effects on immune function in pulmonary tuberculosis. Twenty-one patients with pulmonary tuberculosis completed the 3-month study. Ten of them got 45mg zinc daily and 11 of them got placebo in addition to drug therapy. Immunoglobulins in plasma and cell proliferation, IFN-γ production and CD markers in peripheral blood mononuclear cells (PBMC) were measured. >The immune system of the patients was activated as reflected by the increased concentration of immunoglobulins in plasma. Still, there was no difference in the ability of the PBMC to proliferate and produce INF-γ in response to concanavalin A between patients and controls. Moreover, there were no significant differences in these variables between the zinc-supplemented and placebo groups after 3 months. In other experiments, the addition of zinc sulphate or iron sulphate in vitro to PBMC tended to decrease the number of CD4+ cells. Conclusions The immune system of the tuberculosis patients maintained its activity and in response to pharmacological therapy the immune response seemed to maintain a Th1 orientation. It was not possible to document a role of zinc supplementation for the immune response.