The serum immunoglobulin (IgG, IgM and IgA) concentrations of 52 chlorinated-exposed workers were examined and compared with those of non-exposed, age- and sex-matched individuals. At the time of testing, the exposed population had mean hexachlorobenzene (HCB) blood levels of 3.84 micrograms/dl with a range of 0.1 to 16 micrograms/dl. Increased IgG and IgM levels were found in the HCB-exposed workers (P < 0.05 and P < 0.01, respectively). Hepatic function was evaluated by serum aspartate (AST) and alanine aminotransferase (ALT) activities, as well as by bilirubin levels. IgM concentrations were positively correlated with three of the studied parameters, namely, length of exposure (r = 0.367) and the activities of both AST (r = 0.367) and ALT (r = 0.507).