The ability of Fusarium species to produce fumonisins was studied with 145 isolates of the following species: F. moniliforme (119 isolates), F. subglutinans (12 isolates), F. proliferatum (9 isolates), F. avenaceum (1 isolate), F. oxysporum (1 isolate), and F. semitectum (3 isolates). All isolates were cultured on autoclaved corn kernels. The production of fumonisins was determined by a high-performance liquid chromatography-o-phthaldialdehyde-fluorescence method. Fumonisin production was restricted to isolates of F. moniliforme (94.1%) and F. proliferatum (100%), in the section Liseola, including all strains isolated from wheat, barley, peas, and soybean. One strain of F. proliferatum isolated from maize produced 30,949 μg/g of fumonisin B1and 16,966 μg/g of fumonisin B2.