Toxic Lantana camara taxa growing in Queensland all contain the triterpene acids lantadene A, reduced lantadene A and lantadene B. These when dosed as pure compounds orally to sheep were similarly toxic at 65 to 75, 42 to 80 and 200 to 300 mg/kg body weight respectively, causing jaundice, photosensitisation, kidney and liver lesions typical of natural and experimental lantana poisoning. Because of its comparative toxicity and abundance lantadene A is the most significant toxic principle in the plant. Reduced lantadene A because of its low concentration in the leaves (5% of lantadene A) and lantadene B because of its significantly lower toxicity are thus unlikely to be of much importance in the poisoning of ruminants following consumption of the plant. In addition, the structural features of both lantadene A and B molecules given to sheep by the oral route do not conform to the chemical structures previously reported to be required for liver damaging action of the verbenaceous triterpenes administered to rabbits by the intraperitoneal route.