Extraction and fractionation of toxic cultures of P. viridicatum led to the isolation of viridicatumtoxin. Its chemical properties are reported. The LD50 in rats was found to be 122.4 mg/kg. Hyaline droplet degeneration of the myocardium, renal tubular necrosis and changes in the hepatocytes were observed. Atrophy of the spleen occurred.