SUMMARYForages are often subjected to fungus growth both in storage and in the field and, therefore, may be contaminated with aflatoxin. Aflatoxin-producing strains ofAspergillus flavuswere used to inoculate flasks containing moistened forages. The fungus grew well, causing considerable disintegration of the plant material. The fermented forages were extracted with chloroform for assay, and impurities were removed from extract residues by precipitation from 70% acetone solutions with lead acetate and with hexane from chloroform solutions. Partially purified extracts were chromatographed on thin-layer plates and quantities of aflatoxin determined with a recording densitometer. All forages at 6 days showed the presence of aflatoxin, except red clover and alfalfa. All strains formed aflatoxin on timothy, sweet clover, and oat straw. Aflatoxin B1was produced at levels of 18–52μg/g by NRRL 3145 on sweet clover and oat straw. The highest total aflatoxin (170μg/g) was on oat straw fermented with NRRL 3145, as well as the highest yields of G1, 108μg. Results were confirmed with the duckling assay.