We followed the changes in some parameters in men exposed to asbestos (to chrysotile and in part to crocidolite). The studied group consisted of exposed workers and retired workers who had been exposed to asbestos in the past. The results were compared with those in the control group of unexposed adults and analysed according to age, duration of exposure, smoking habits and radiological findings. Investigated were: the levels of immunoglobulins IgA, IgG, IgM, complement components C3, C4, alpha-1-antitrypsin and transferrin (humoral immunity) as well as the phagocytic activity of the leukocytes in peripheral blood (natural immunity). The comparison of the results with those in the control group showed that asbestos exposure stimulated markedly IgG and C4 production and to a lesser extent also IgA, IgM, C3 and transferrin production and it suppressed natural immunity. Comparison of the results of the same age categories--control (40.8), with the subgroup of active workers (44.4), showed significantly increased levels of IgA, IgG, IgM, C4 and decreased values of natural immunity in asbestos exposed group. Comparison of different age categories (pensioners--63.2: workers--44.4) showed, that from five parameters in which statistically significant differences were found, four had decreased values in pensioners. Radiological findings suggested, that changes in immunological parameters probably preceded pathologic processes. There were statistically significant differences in the levels of IgM in smokers compared with nonsmokers in the subgroup of workers exposed to asbestos and in the levels of IgG and C4 in the group of workers + pensioners together. It follows from the present study that asbestos exposure modulates the immune response and leads to significant changes of humoral and natural immunity.