The effects of the new anti-platelet agent KBT-3022, ethyl 2-[4,5-bis(4-methoxyphenyl)-thiazol-2-yl]pyrrol-1-ylacetate, and its metabolite desethyl KBT-3022 on rabbit neutrophil function were investigated in comparison with the effects of acetylsalicylic acid (ASA), ticlopidine hydrochloride (TP), cilostazol (CIL) and indomethacin (IM). The adhesion and migration of neutrophils induced by formyl-methionyl-leucyl-phenylalanine (fMLP) were inhibited by all the compounds tested, their rank order of potency being KBT-3022 = desethyl KBT-3022 > TP = CIL = IM > ASA. KBT-3022, desethyl KBT-3022, CIL and IM all suppressed fMLP-induced increases in the intracellular free Ca2+ concentration ([Ca2+]i) in neutrophils, their potencies correlating with their inhibitory effects on fMLP-induced adhesion and migration. KBT-3022 (1 microM), desethyl KBT-3022 (1-10 microM) and CIL (10 microM) but not IM significantly inhibited both neutrophil migration and the increase in [Ca2+]i induced by leukotriene B4 (LTB4). KBT-3022 (1 microM) and desethyl KBT-3022 (1 microM) suppressed the increase in [Ca2+]i induced by complement C5a. Although KBT-3022 and desethyl KBT-3022 did not influence [3H]LTB4 and [125I]C5a specific binding, [3H]fMLP specific binding was inhibited by desethyl KBT-3022 (IC50: 1.9 microM). Neutrophil adhesion and superoxide anion production stimulated by phorbol 12-myristate 13-acetate were partially inhibited by KBT-3022 (1 microM) and desethyl KBT-3022 (1-10 microM). These results suggest that KBT-3022 and desethyl KBT-3022 have a wider spectrum of action and are more potent inhibitors of neutrophil activation than ASA, TP, CIL and IM.