Three patients presented respiratory abnormalities following Crotalus durissus snakebite. These abnormalities appeared in the first 48 h after the snake bite and consisted of dyspnea, tachypnea, use of accessory muscles of respiration (cases 1 and 2) and flaring of the nostrils (case 2). Cases 1 and 2 developed acute respiratory failure. Case 2, 24 h after the snakebite presented difficult breathing and periods of apnea. He was intubated in the emergency room and transferred to the intensive case unit where he arrive with spontaneous breathing. His respiratory pattern worsened and measurement of arterial pH and blood gases showed metabolic and respiratory acidosis with partial carbon dioxide pressure increasing from 40 to 50,3 mmHg compatible with acute ventilatory failure. Both patients needed mechanical ventilation. Weaning from the ventilator was accomplished after 33 days in case 1 and after 15 days in case 2. Both patients also presented acute renal failure treated with peritoneal dialysis with full recovery of the renal function. Measurements of forced vital capacity (FVC) and forced expiratory volume in the first second (FEV 1.0) was carried out 58 hours after the snakebite in case 3. Both FVC and FEV 1.0 were reduced in relation to the predicted values (60 and 67% respectively) but the ratio FEV 1.0/FVC was in the normal range. These findings were compatible with a restrictive pattern of ventilatory failure. Serial measurements showed progressive increase of both FVC and FEV 1.0 reaching 72 and 79% of the predicted values, respectively, in the 10 th day after the snakebite. Case 1 developed deep coma attributed to cerebral hypoxia suffered during several episodes of seizure and died of pulmonary infection 10 months after the snakebite. Cases 2 and 3 recovered completely. These respiratory abnormalities were attributed to the action of crotoxin in the respiratory muscles since the patients did not present complications such as severe uremia, atelectasis, pulmonary infection, cardiac failure and pulmonary edema that could also produce them.