Maize samples were obtained from different locations-namely Aba, Abakaliki, Afikpo, Okigwe, and Owerri-all in southeast Nigeria. Twelve mold species of the genera Aspergillus, Penicillium, Cladosporium, Alternaria, Fusariurn, and Acremoniurn (Cephalosporiurn) were isolated. The presence of aflatoxin B, was detected in 80% of the samples by the characteristic blue fluorescence that appeared on silica gel coated thin layer chromatography plates when viewed with a long-wave ultraviolet radiation source alongside an aflatoxin standard. Eight isolates of the Aspergillus flavus group obtained from the maize samples were tested for aflatoxin production. Natural medium (maize) at 26°C and moisture content adjusted to no less than 20% was used. Aflatoxin was produced to some degree by 87.5% of the isolates. There was no aflatoxin production at a market moisture content of 5.4% and temperature of 25, 30, and 35°C. However, at 26°C and increased moisture contents of 22.3-24.9%, varying amounts of aflatoxin were produced. 0 7994 byJohn Wiley & Sons, Inc.