A model in Wistar rats (n = 30, 279-345 g) was developed to study circulatory, respiratory, metabolic, and lethal effects of an intravenous infusion (30 min; 1.25, 1.5, 1.75, and 2.0 mg/kg) of rattlesnake (Crotalus viridis helleri) venom. Venom produced perfusion failure with lactacidemia, hemoconcentration, hypoproteinemia, and death. The severity of poisoning was proportional to the quantity of venom given and to the elevation in lactic acid and hematocrit. Hemorrhages in the diaphragm, intercostal muscles, and intestine were observed at necropsy. In a separate test, rats (n = 12, 311-355 g) received an infusion of 1.5 mg/kg of venom or physiological salt solution. Blood volume was measured 30 min after the end of infusion in both groups with radioiodinated (125I) human serum albumin (RIHSA) and 51Cr-labeled rat red cells. Venom produced a significant reduction in total blood volume index (35%, P less than 0.001), plasma volume index (46%, P less than 0.001), and red cell mass indec (22% P less than 0.005). The slope of the RIHSA-disappearance curve of animals that received venom was more than twice that of the control group. We conclude that perfusion failure following rattlesnake envenomation is associated with hypovolemia due to increases in vascular permeabiltiy and hemorrhage.