Antibodies against cytoplasm of neutrophil leucocytes (ANCA) with a high sensitivity are found in idiopathic necrotizing vasculitis and idiopathic glomerulonephritis with formation of sickles (IGS). C-ANCA are directed against the myeloid lysosomal enzyme--proteinase 3 and are found above all in Wegener's granulomatosis and microscopic polyarteritis. P-ANCA are directed mainly against myeloperoxidase, less against leucocytic elastase or lactoferrin and are found above all in microscopic polyarteritis, IGS, polyarteritis nodosa or Churg-Strauss syndrome. The elevated ANCA level correlates with the activity of the disease or precedes a relapse. These autoantibodies activate probably neutrophil leucocytes for respiratory exacerbation and degranulation which may lead to extensive tissue damage.