Serine proteinase inhibitors, in the seeds of several Leguminosae from the Pantanal region (West Brazil), were studied using bovine trypsin, a digestive enzyme, Factor XIIa and human plasma kallikrein, two blood clotting factors. The inhibitors were purified from Enterolobium contortisiliquum (M(r) = 23,000), Torresea cearensis (M(r) = 13,000), Bauhinia pentandra (M(r) = 20,000) and Bauhinia bauhinioides (M(r) = 20,000). E. contortisiliquum inhibitor inactivates all three enzymes, whereas the T. cearensis inhibitor inactivates trypsin and Factor XIIa, but does not affect plasma kallikrein; both Bauhinia inhibitors, on the other hand, inactivate trypsin and plasma kallikrein but only the B. pentandra inhibitor affects Factor XIIa. Ki values were calculated between 10(-7) and 10(-8) M.