Mycelial growth and production of aflatoxins by Aspergillus parasiticus NRRL A-16,462, on whole peanuts, undelintered cottonseed, and shredded wheat was compared to growth and aflatoxin production on 10% broths of the same substrates. The greatest amount of toxins was produced on shredded wheat as a whole substrate. The least amount was produced in shredded wheat broth medium. Intermediate levels of toxin were produced on cottonseed in both types of media. More aflatoxin was produced on peanut broth than on whole peanuts. Mycelial growth on whole shredded wheat was greater than growth on the other solid media though it had the lowest amount of growth of the three broth media. Among whole substrates, growth on fuzzy cottonseed was least but mycelial growth on cottonseed broth was second of the three broth media. Growth on whole peanuts was as great as on shredded wheat; on peanut broth, it was the greatest of the three broth media. On whole substrates, the ratio of aflatoxins B:G produced was highest on shredded wheat and lowest on peanuts. In broth culture the B:G ratio was largest on the cottonseed and lowest on shredded wheat.