The polyvalent antivenom produced at the Instituto Clodomiro Picado, Costa Rica, was tested for its capacity to neutralize proteolytic and hemorrhagic activities of ten Costa Rican crotaline venoms. In experiments with preincubation of venom and antivenom, the latter efficiently neutralized proteolytic activities of nine venoms, with ED50 ranging from 50 to 300 microliters antivenom/mg venom. The venom of Bothrops nummifer was neutralized less efficiently (ED50 = 760 microliters/mg.) Antivenom was also very effective in neutralizing hemorrhagic activity, having its lowest neutralizing ability against the venom of B. picadoi (ED = 430 microliters/mg) and its highest towards the venom of B. asper (Pacific region) (ED50 = 47 microliters/mg). There was a significant correlation between the ability of antivenom to neutralize proteolytic and hemorrhagic effects. In spite of the ability of antivenom to neutralize hemorrhage when incubated with venom prior to injection, hemorrhage was only partially neutralized when antivenom was administered i.v. at different time periods after envenomation. This suggests that the rapid development of local hemorrhage, instead of the absence of antivenom antibodies, is the explanation for the poor neutralization observed in these types of experiments.