To assess the immune competence of workers occupationally exposed to mainly silica, peripheral blood lymphocytes, serum immunoglobulins (IgG, IgA and IgM), C3 and C4 complement protein concentrations of foundry and pottery workers were evaluated and compared to healthy controls with no history of silica and other chemical exposure. The absolute number and percentage of functionally different subsets of peripheral blood mononuclear lymphocytes, i.e. T, T-suppressor and natural killer cells were unchanged. However, T-helper lymphocytes in pottery (P<0.05) and B cells in foundry (P<0.01) workers were significantly lower when compared to their controls. In addition, silica-exposed foundry workers had a significant reduction in the IgG, IgA and IgM levels. No significant differences were observed in the serum complement C3 and C4 levels of the workers. These results suggest that human chronic exposure to mainly silica and other chemicals originating from foundry and pottery settings may be detrimental to the immune system.