A total of 260 isolates, including 43 species of Penicillium and 7 species of Aspergillus, were screened for their ability to produce aflatoxin on rice. Chloroform extracts were analyzed by thin-layer chromatography. None of the isolates produced aflatoxin. Certain species of Penicillium produced fluorescent substances that either were similar in R(F) or were of similar color to B and G aflatoxins. These substances were subsequently proved not to be aflatoxin by two-dimensional chromatography, by reaction with iodine fumes, or by both methods.