LD50 studies of viridicatumtoxin were done in rats and mice using oral, intraperitoneal (i.p.), and subcutaneous (s.c.) routes. Mice were given oral doses of viridicatumtoxin up to 350 mg/kg body weight and rats were given doses of viridicatumtoxin up to 150 mg/kg. No deaths occurred in the animals dosed by the oral route. Hepatic alterations of hydropic change and necrosis of centrolobular hepatocytes were observed in mice given 250, 300, or 350 mg/kg viridicatum toxin and were more severe in the mice given the higher doses. No histopathologic alterations were present in the rats dosed orally. Mice were given doses of viridicatumtoxin up to 300 mg/kg, s.c., and rats up to 400 mg/kg. No deaths occurred in the animals dosed by this route. Microscopic alterations in both mice and rats were limited to the injection sites and consisted of coagulation necrosis. The single-dose, 72-h i.p. LD50 for the mouse and the rat was 70 mg/kg and 80 mg/kg respectively. Histopathologic alterations in mice given viridicatumtoxin i.p. included fibrinous peritonitis, large subcapsular areas of hepatic necrosis, single-cell hepatocytic necrosis, splenic lymphoid depletion, and vacuolar degeneration of the myocardium. Rats had splenic lymphoid depletion and fibrinous peritonitis.