A crude extract containing some toxic furanoterpenoids was isolated from F. solani infected sweet potatoes. Chronic administration of the crude extract to male albino rats at a dosage of 1 mg/kg body weight/day for 21 days brought about a sharp increase in the thiobarbituric acid reactive substances and a depression of glutathione levels in the lung and liver homogenates. The antioxidant defense system was affected as evident from a significant fall in the activities of the enzymes, superoxide dismutase, catalase, glutathione peroxidase, glucose-6-phosphate dehydrogenase and glutathione-S-transferase. Such an alteration could be the reason for the lung and liver damage caused by these toxic furanoterpenoids.