Aspergillus oryzae (ATCC, 12892) was studied for its ability to produce Beta-Nitropropionic Acid (BNP) in selected high protein and carbohydrate-rich foods. Portions of 35 grams of white potato, yellow sweet potato, ripe banana, freshly made Indonesian tempeh, and Cheddar cheeses loosely packed in petri dishes were inoculated with a spore suspension of A. oryzae . In Blue and Camembert cheese samples, the test organism was added along with the penicillium molds during manufacture. Ten imported mold-ripened cheeses obtained from a retail outlet in New York City were also tested. All food specimen were assayed for BNP. The Aspergillus contaminant did not produce BNP in Camembert and Bleu cheeses; but in Cheddar, production occurred when mold contaminated cheese was maintained at approximately room temperature. Indonesian tempeh provided a poor substrate for the production of this mold toxin, but A. oryzae flourished on cooked sweet potato, white potato and ripe banana and produced BNP. Synthesis in yellow sweet potato was significantly less than in the other carbohydrates.