Mice killed shortly after receiving 1300–3000 spores of Clostridium botulinum type C per os were incubated at one of four chosen temperatures together with bottles of cooked meat medium seeded with a similar inoculum. After incubation the rotting carcasses were homogenized. Sterile membrane filtrates of the homogenates (10–20.8%, w/v) and pure cultures were then titrated for toxicity. A temperature of 37 °C produced less toxicity in most carcasses than in cultures. At 30 °C, however, toxicity (often 2× 105 to 2× 106 mouse intraperitoneal LD/g or ml) was roughly similar in both systems, and some carcasses and cultures were still toxic (2× 104 to 2× 105 LD/g or ml) after 349 days. Surprisingly, at 23 °C, though greatly reduced in the cultures, toxicity was high in many carcasses for at least 28 days. Little or no toxin was produced in either system at 16 °C. Unfiltered homogenates (17·8–22·5%, w/v; dose 0·25 ml per os) of toxic carcasses incubated at 30 °C for 7 days invariably produced death from botulism, often within as little as 4 h, but a 1 in 10 dilution produced less than 100% mortality.