The genus Aspergillus section Nigri, or the black aspergilli, represents genetically closely related species that produce the mycotoxins, ochratoxins and the fumonisins. Fumonisin B1 (FB1) is of an added concern because it is also a virulence factor for maize. Our preliminary data indicated that black aspergilli could develop asymptomatic infections with maize and peanuts plants. Symptomless infections are potential problems, because under favorable conditions, there is a potential for accumulation of ochratoxins and the fumonisins in contaminated postharvest crops. In the present report, the ability of black aspergilli from peanuts and maize to produce ochratoxin A and FB1 on maize kernels was assessed. One hundred fifty strains from peanuts and maize were isolated from several southeastern and midwestern states. Aspergillus nigri (A. nigri var. nigri) was the dominant species (87%), while Aspergillus foetidus, Aspergillus japonicus, Aspergillus tubingensis, and Aspergillus carbonarius were infrequently isolated. None of the wild isolates produced detectable amounts of ochratoxins. However, we do report the occurrence of the fumonisins B1, B2, and B3. Of 54 field isolates, 30% (n = 16) produced FB1, 61% (n = 33) produced FB2, and 44% (n = 24) produced FB3. The amounts of fumonisins produced during the test period of 30 days suggest that these strains might be weak to moderate producers of fumonisin on maize. To our knowledge, this is a first report of FB1 and FB3 production by isolates of black aspergilli from an American cereal and legume.