Anti-neutrophil cytoplasm antibody (ANCA) has been shown to be no marker of systemic lupus erythematosus (SLE) including lupus nephritis or of progressive systemic sclerosis (PSS). Antibodies against myeloperoxidase (anti-MPO) and elastase, two granulocyte lysosomal enzymes, were found in patients with SLE but not in those with PSS, except for one patient who had anti-MPO. Anti-MPO was present in 21% of patients with SLE, and at low concentrations in about 80% of these cases. Anti-elastase was found in four patients with SLE. In another group of six patients with a SLE-like syndrome induced by anti-hypertensive treatment with the anti-hypertensive hydralazine, anti-MPO antibodies occurred in all six, and anti-elastase antibodies in five. Monitored during a 2-year follow-up period, anti-MPO antibodies were found to persist, whereas anti-elastase antibodies were rapidly eliminated, after withdrawal of the drug.