1. The edema-forming activity of eight Costa Rican crotaline snake venoms and its neutralization by a polyvalent antivenom were studied using the mouse footpad test.
2. All of the venoms induced edema, the highest activity being present in the venoms of Bothrops lateralis and Bothrops picadoi.
3. When experiments were performed with preincubation of venom and antivenom, neutralization of edema was poor. Moreover, it was observed that, with some venoms, edema increased when large doses of antivenom were used. This effect was also observed when some venoms were incubated with coral snake antivenom, suggesting that venoms may release some pharmacologically active component(s) from antivenom, since the latter contains traces of alpha-2 and beta globulins.
4. Based on these findings, an alternative approach to the study of the neutralization of edema was used; in this new method, antivenom was injected i.v. before venom administration, thereby avoiding preincubation. With this technique, a much better neutralization of edema was observed, although with some venoms it was still poor.
5. Venoms contain low molecular weight factors which induce edema, suggesting that lack of immunogenicity of some components may cause a poor neutralization. However, such components are responsible for only a minor portion of the edema induced by crude venoms.
6. It is suggested that experiments in which venom and antivenom are preincubated in testing the neutralization of edema should be avoided, and that a more adequate approach may be an independent inoculation of venom and antivenom.