Four groups of silicotic patients were examined including 34 miners who had radiologically manifest fibrosis following exposure for 15 years, 40 miners who demonstrated no radiological signs of silicosis even after exposure for more than 30 years, 48 stone masons and quarriers, and a referent group of 25 nonexposed men. Lysozyme, angiotensin converting enzyme, and fibronectin revealed significantly higher values in coal mine workers with and without pneumoconiosis in comparison to the referent group. Effects on humoral immunity were noted by an increase of complement component C3 and in part by an increase of immunoglobulin-G (IgG) and immunoglobulin-A (IgA). Autoimmunity phenomena were demonstrated by occurrence of antinuclear antibodies and of circulating immune complexes, containing C3, IgG, IgA, and immunoglobulin-M. These alterations occurred not only in miners where silicosis was manifest, but also in miners without radiologically detectable fibrosis. Quartz containing dusts stimulated not only those functions of the macrophages which were involved in fibrosis, but also resulted in immunoregulatory dysfunctions detectable before the incidence or independently of a clinical manifest fibrosis. As demonstrated by incidence of antinuclear antibodies, the quality of quartz containing dust has a great influence on the manifestation of autoimmunity phenomena.