AbstractMaize samples were obtained from different locations—namely Aba, Abakaliki, Afikpo, Okigwe, and Owerri—all in southeast Nigeria. Twelve mold species of the generaAspergillus, Penicillium, Cladosporium, Alternaria, Fusarium, andAcremonium (Cephalosporium)were isolated. The presence of aflatoxin B1was 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 theAspergillus flavusgroup 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. ©1994 by John Wiley