Pretreatment with captopril, a kininase II inhibitor, at 10 mg/kg i.p. or s.c., significantly increased the writhing response induced by a minimum effective dose (0.75 mg/kg i.p.) of phenylbenzoquinone (PBQ), by 91–148%. 1,10-Phenanthroline, a carboxypeptidase B inhibitor (2 mg/kg i.p.), in combination with captopril enhanced the algesic effect of PBQ by 309–360%. Captopril also doubled the number of writhes induced by a minimum effective dose of BK (5 μg/kg i.p.) in PGE₂-pretreated mice. The writhing responses induced by higher doses of PBQ or BK were not affected by these inhibitors. The hyperalgesic effect of BK (1 μg) injected into the hindpaw of rats was significantly increased and prolonged by coinjection of captopril (30 μg) and 1,10-phenanthroline (30 μg) and was prevented by carboxypeptidase B (1 mg). These data indicate that BK plays a role in pain in these models, a role which appears of greatest relevance at threshold algesic stimulation.