Mice were treated per os with one oral LD100 of toxic filtrate from a culture of Clostridium botulinum type C. The period between dosing and the first appearance of clinical signs varied greatly (2-31 h) from one animal to another. The duration of the pre-clinical and clinical phases together ranged from 5.5 to greater than 55 h. The duration of the clinical phase alone ranged from 1.25 to greater than 24 h, except for a minority of mice in which death occurred suddenly from apparent heart failure with no premonitory signs 4.75-31 h after dosing. Toxaemia was demonstrable in all mice that had just begun to show a clinical response 3.75-6.5 h after dosing, and in some that had not. Outside these time limits toxaemia was demonstrable only rarely, and beyond 12 h after dosing never. Therefore the many (approximately 50%) mice that began to show clinical signs more than 12 h after dosing had no demonstrable toxaemia throughout the entire clinical phase of the disease. The concentrations of toxin demonstrated in the blood ranged from less than 5 to greater than or equal to 20 (but less than 40) intravenous mouse-lethal doses/ml.