Rapidly progressive glomerulonephritides (RPGN) are forms of necrotizing glomerulonephritis associated with anti-glomerular basement membrane (anti-GBM) and anti-neutrophil cytoplasmic antibodies (ANCA) against the antigens proteinase-3 (anti-PR3) and myeloperoxidase (anti-MPO). RPGN have a course of rapid progression to renal failure. We compared the results from the semiquantitative ELISAs for anti-GMB antibodies, PR3-ANCA and MPO-ANCA and the indirect immunofluorescence technique (IIF) against a new rapid assay (30 minutes) for the same antibodies in patients with clinically suspected RPGN. The semiquantitative ELISAs for anti-GBM antibodies and PR3-ANCA and MPO-ANCA have a proven diagnostic significance in patients with RPGN I and III. There were no significant differences between the ANCA-GBM screening test and the results from the semiquantitative ELISAs (p > 0.05). We did not find significant differences between the results for PR3-ANCA and MPO-ANCA from the ANCA-GBM screening test with C-ANCA and P-ANCA IIF values (p > 0.05). We also corroborated that the ANCA-GBM screening test is a diagnostic tool for RPGN I and III as useful as the semiquantitative ELISAs and the IFF technique. The ANCA-GBM ELISA screening test is a tool as useful as the semiquantitative ELISA against anti-GBM antibodies for diagnosis of RPGN I. The comparison of the screening ELISA with the IIF technique and the semiquantitative ELISAs against PR3-ANCA and MPO-ANCA showed similar utility for diagnosis of RPGN III. The advantages of the new screening assay are that three antibodies are tested at the same time, yielding results in only 30 minutes.