In the State of Amazonas and in areas nearby Manaus, the snakes responsable for the majority of accidents are Bothrops atrox and Lachesis muta muta, with a percentage of confirmed species of 76% and 17%, respectively. Frequently, in the absence of the laquetic and bothropic-laquetic antivenoms, the Instituto de Medicina Tropical de Manaus (IMTM) has been using bothropic antivenom in the treatment of laquetic accident. In this paper is related a case of accident caused by L. muta muta; the patient was treated with bothropic antivenom, and after received twenty ampoules of this antivenom, mantained blood incoagulability until the 13th day after the accident. Experiments to obtain the potency of the bothropic antivenom for the coagulant and hemorrhagic activities has been done, using Bothrops atrox venom as control. The results showed that the potency of the antivenom for the hemorrhagic activity was similar, and the potency for the coagulant activity for the L. m. muta venom was 9.2 times minor than that for B. atrox. The antibodies titles from three different lots of bothropic antivenom varied for the L. m. muta venom, and were constant for the B. atrox venom. Due to the inefficiency of the bothropic antivenom on the neutralization of the coagulant activity for the L. m. muta venom, the use of bothropic antivenom is not recomended in the treatment of Lachesis muta muta accidents.