The Saw-scaled or Carpet Viper (Echis carinatus) whose range extends from Senegal to Bengal probably bites and kills more people than any other species of snake. One hundred and fifteen patients with poisoning caused by its bite were studied in the savanna region of Nigeria, where victims of this snake may occupy 10 per cent of hospital beds. Patients showing no signs of envenoming were excluded. All patients had local swelling at the site of the bite. Other features included local blistering (13 per cent), local necrosis (11 per cent), incoagulable blood (93 per cent), and spontaneous systemic bleeding (57 per cent). There was evidence of disseminated intravascular coagulation in all cases; fibrinogen was severely depleted, fibrin degradation products were increased (mean 1711 +/- 904 micron per ml), but significant thrombocytopenia (less than 103 000 per mm3) was seen in only ten severe cases. Clotting factors V, VIII, II and XIII were depleted, while X and VII were usually normal. Fibrinolytic activity was rarely increased, so it seems likely that a procoagulant action (direct activation of prothrombin) is principal effect of E. carinatus venom on blood coagulation in man. Development of the haemostatic defect was observed as early as 75 minutes and as late as 27 hours after the bite. Spontaneous haemorrhage is clinically the most important effect of E. carinatus venom, causing the five deaths in this series. The relative importance of procoagulant and haemorrhagic components of the venom in causing haemorrhage is discussed. Complement activation via the classical and alternative pathways may have contributed to vascular damage. Mortality was reduced from the untreated level of between 10 and 20 per cent to 2.8 per cent in a group of 107 patients treated with 10 to 110 ml of specific antivenom. The dose was controlled using a simple clotting test. Blood coagulability was restored in two to 39 (mean 12) hours after the first dose of antivenom. Immediate-type serum reactions were observed in 21 per cent of cases. Additional treatment included blood transfusion for patients in haemorrhagic shock and ealry surgical débridement of necrotic tissue at the site of the bite.