This review discusses the main issues of antineutrophil cytoplasm autoantibodies (ANCA) that have emerged from the literature. From January 1997 to August 1998, 216 papers were published on ANCA. Two major themes seem to be evolving from these articles. The first theme concerns the specificity and sensitivity of ANCA testing in clinical practice in relation to diagnosing systemic vasculitic syndromes. We focus on immunofluorescence patterns, ANCA antigens, testing methodology, and the (predictive) value of ANCA in clinical practice. Second, there is the unsolved question of how ANCA are etiologically involved in the development of the vasculitic lesion. Ongoing research questions the role of ANCA in stimulating granulocytes, monocytes, and the endothelium.