Neutralization of lethal toxicity (50% effective dose; ED50), hemorrhagic (minimum hemorrhagic dose; MHD) and hemolytic activity (PLA2) and levels of antibodies, measured by enzyme-linked immunosorbent assay (ELISA), were investigated to test the potency of horse antibothropic serum (ABS) against Bothrops venoms from the Amazonian rain forest. ABS neutralized the lethal activity with a potency (mg of venom neutralized per 1 ml of antivenom) of 5.5, 3.7, 1.6, 1.3 and 6.5, respectively, for B. jararaca (reference venom for assessing the ABS potency in Brazil), B. atrox, B. brazili, B. bilineatus smaragdinus and B. taeniatus venoms. The volume of antivenom (μl) that neutralized one MHD of B. jararaca, B. atrox, B. brazili, B. bilineatus smaragdinus and B. taeniatus venoms was 5, 7.71, 7.76, 8.3 and 5, respectively. ABS neutralized the PLA2 activity with a potency of 6.2, 3.2, 1.4, 2.6 and 5 respectively, for B. jararaca, B. atrox, B. brazili, B. bilineatus smaragdinus and B. taeniatus venoms. ELISA reactivity of ABS against the separate venoms was found to be quite variable. The reactivity against B. jararaca venom was higher than against other Bothrops venoms. In conclusion, the assays described here suggest that Brazilian Bothrops polyspecific antivenom is not very efficient in neutralizing the effects of venom from some Amazonian Bothrops species. Copyright (C) 2000 Elsevier Science Ltd.