Fusarium subglutinans is an important pathogen of maize and other commodities worldwide. We examined MRC-115 and 71 other F. subglutinans strains from various geographic areas for their ability to synthesize fusaproliferin, a novel toxic sesterterpene recently isolated from F. proliferatum. Fusaproliferin production ranged from 30 to 1,500 μg/g of dried ground substrate, with 33 strains producing more than 500 μg/g. In particular, strain MRC-115 produced as much as 1,100 to 1,300 μg/g. In toxicity studies of two invertebrate models, fusaproliferin was toxic to Artemia salina (50% lethal dose, 53.4 μM) and to the lepidopteran cell line SF-9 (50% cytotoxic concentration, approximately 70 μM, after a 48-h exposure). Fusaproliferin was also toxic to the human nonneoplastic B- lymphocyte cell line IARC/LCL 171 (50% cytotoxic concentration, approximately 55 μM in culture in stationary phase after a 48-h exposure). Experiments performed with cells exposed at seeding suggested a possible cytostatic effect at subtoxic concentrations.