Thirty-eight production workers exposed to Ni and 35 exposed to Co were examined for the content of Ni and Co in hair, the serum concentration levels of immunoglobulins, IgG, IgA, IgM, and IgE, and serum proteins, alpha 2-macroglobulin (A2M), transferrin (TRF), alpha 1-antitrypsin (A1AT), ceruloplasmin (CPL), lysozyme (LYS), and alpha 1-glycoprotein (A1GP). Atomic absorption analysis of hair revealed that the respective geometric mean values of Ni and Co in Ni-exposed workers were 216.75 and 3.31 micrograms X g-1 and in Co-exposed workers 34.5 and 96.81 micrograms X g-1. These values were significantly higher than respective control values found in nonexposed individuals matched by age (Ni: 3.31 and Co: 0.38 micrograms X g-1). These findings suggest that hair analysis is a suitable method for the biological monitoring of exposure to these two metals. Tests for serum proteins revealed that nickel workers differed from controls by exhibiting significantly elevated IgG, IgA, and IgM levels; cobalt workers by a significant elevation of IgA level; and both exposed groups by a significant drop in the IgE level. A significant rise in the concentration (P less than 0.001-P less than 0.005) was also recorded in the case of A1AT, A2M, CPL, and LYS. The possible biomedical implications of these immunobiochemical findings are critically analyzed.