In a 59-year old sand-blaster, histologically proven silicosis was complicated by systemic lupus erythematosus (SLE) and focal glomerulonephritis with IgG, IgA and ClQ deposits. Nothing likely to facilitate SLE was detected by investigating the familial background, the HLA phenotype and the complement system. This type of SLE differs from drug-induced lupus-like syndromes by a high level of anti-double helix DNA antibodies and by the renal lesions observed. The connection between silicosis and SLE lies in changes in humoral immunity, i.e. polyclonal activation and production of antinuclear antibodies. A decrease in the number of suppressor T-cells may also be held responsible.