Five isolates of Fusarium moniliforme and two isolates Fusarium proliferatum of the Section Liseola were each fermented on rice for 21 d at 25 C. Each Fusarium-fermented rice, when dried and mixed into a poultry diet (10% by weight), caused a varied degree of acute mortality in baby Pekin ducklings. The acute (death in less than 48 h) mortality correlated significantly only to the amount of moniliformin in fermented rice, thus in the diet, but not to the amount of fumonisin B-1 in fermented rice. This correlation of moniliformin concentration and noncorrelation of fumonisin B-1 concentrations to acute toxicity were confirmed by duckling assay using diets containing these purified mycotoxins.