Antivenoms are the currently available agents for treatment of snake venom intoxication. The development of therapeutic strategies employing more generally available drugs could improve treatment of invenomation by reducing hypersensitivity reactions, cost and storage requirements. I report that chloroquine reduced the toxicity in mice of the venom from the Formosan krait, Bungarus multicinctus, when both venom and drug were administered i.p. When chloroquine was injected immediately after the injection of venom, the median lethal dose (LD50) of the venom was increased 5-fold from 19 to 95 micrograms/kg. Investigation of chloroquine's effect on the purified neurotoxic components of B. multicinctus venom revealed that chloroquine increased the LD50 of beta-bungarotoxin 17-fold, from 7.8 to 134 micrograms/kg but had little effect on the LD50 of alpha-bungarotoxin. Chloroquine was an effective antagonist of the toxicity of B. multicinctus venom and of purified beta-bungarotoxin without itself being overtly toxic.