The antinephritic effect of DP-1904 [6-(1-imidazolylmethyl)-5,6,7,8-tetrahydronaphthalene-2-carboxylic acid hydrochloride], a thromboxane (TX) A2 synthase inhibitor, was compared with that of OKY-046 and azathioprine, using an experimental model of nephritis, crescentic-type anti-glomerular basement membrane (GBM) nephritis. Test drugs were given p.o. once daily from an autologous phase in which proteinuria was already fully developed. DP-1904 (15 and 45 mg/kg per day) and OKY-046 (20 mg/kg per day), another TXA2 synthase inhibitor, significantly inhibited the development of glomerular alteration as well as the elevation of proteinuria. On the other hand, azathioprine (20 mg/kg per day), an immunosuppressive agent, failed to suppress the proteinuria. A single administration of DP-1904 or OKY-046 inhibited glomerular TXB2 production and increased glomerular prostaglandin (PG) E2 and 6-keto PGF1 alpha production in nephritic rats. Both drugs apparently decreased the depositions of both rabbit immunoglobulin (Ig) G and rat IgG on GBM in nephritic rats, but azathioprine inhibited only the deposition of rat IgG. These results suggest that DP-1904 may be an effective agent for the treatment of proliferative glomerulonephritis and its antinephritic effect may be due to the amelioration of abnormal metabolism of arachidonic acid.