Gibberella fujikuroi strains isolated from rice in the United States, Asia, and other geographic areas mere tested for sexual fertility with members of mating population D and for production of fumonisin B-1 and moniliformin in culture. Of the 59 field strains tested, 32 (54%) were able to cross with tester strains of mating population D, but only a few ascospores were produced in most of these crosses, Thirty-four strains produced more than 10 mu g of fumonisin B-1 per g, hut only three strains produced more than 1000 mu g/g. Twenty-five strains produced more than 100 mu g of moniliformin per g, and 15 produced more than 1,000 mu g/g. Seven held strains produced both fumonisin B-1 and moniliformin, but none of these strains produced a high level of fumonisin B-1 (>1,000 mu g/g). However, a genetic cross between a strain that produced fumonisin B, but no moniliformin and a strain that produced moniliformin but no fumonisin B-1 yielded progeny that produced high levels of both toxins, Strains of G. fujikuroi isolated from rice infected with bakanae disease are similar to strains of mating population D isolated from maize in their ability to produce both fumonisins and moniliformin, This finding suggests a potential for contamination of rice with both fumonisins and moniliformin.