Circulating autoantibodies, namely c-ANCA, MPO-ANCA, anti-Goodpasture (anti-NC1), and anti-entactin antibodies were analysed in sera from 82 consecutive patients with crescentic involvement of more than 50% glomeruli in renal biopsy specimens. Sixty-eight (approximately 83%) patients possessed one or more of these autoantibodies. About two-thirds of all patients had ANCA (c-ANCA, MPO-ANCA or both). Most of the remaining positive patients had anti-NC1 antibodies. Very few patients had anti-entactin antibodies, thereby suggesting a poor association of these antibodies with extracapillary glomerulonephritis (ECGN). Thus two different categories of patients, one possessing ANCA and the other anti-NC1 antibodies, could be recognised. Patients with anti-NC1 antibodies were characterised by linear immune deposits along the glomerular basement membrane and the clinical outcome was invariably grim. On the other hand, despite no significant difference in renal morphology from patients with anti-NC1 antibodies, the disease in patients with ANCA, in general, had a milder course. Among patients with ANCA, those with c-ANCA mainly had systemic small-vessel vasculitis with widespread systemic manifestations, whereas most patients with renal restricted primary ECGN with non-linear immune deposits possessed MPO-ANCA. Furthermore, patients with c-ANCA had a more severe disease than those with MPO-ANCA. These observations indicate that a continuous spectrum of diseases exists between idiopathic small-vessel vasculitides and primary non-linear ECGN. Our study also demonstrates that the presence of auto-antibodies is a dominant feature of severe ECGN and that the type of immunological injury is more important than the extent of crescentic involvement of glomeruli in determining the course of illness in patients with ECGN.