12,13-epoxytrichothec-9-en-8-one) is a naturally occurring trichothecene toxin produced by several Fusarium fungi that parasitize numerous cereal grains. Numerous species of Fusarium have been found to produce DON. The genus Fusarium occurs throughout the world and may affect corn, wheat, barley, oats, rice, and sorghum and complete feed formulations. Cereal grain contamination by DON occurs most frequently when conditions are cool and wet at the time of grain formation and harvest and is associated predominantly with infection in the field rather than as a complication of storage. 7 Although most descriptions of widespread grain contamination by DON have been confined to temperate zones of the world, DON contamination has also been reported to affect grain in subtropical climates. Deoxynivalenol has been given the trivial name vomitoxin because it causes emesis when ingested by swine and dogs. Other clinical effects attributed to the toxic effects of ingested DON include feed refusa1, decreased weight gain, signs of gastrointestinal irritation (e.g., diarrhea, colic, rectal prolapse, hematochezia), thickening of the squamous aspect of the gastric lining of pigs, reproductive problems, skin irritation, cardiotoxicity, and interference with the immune system. 16 The extent to which DON causes clinical signs of toxicosis is proportional to its concentration in contaminated feed. Ingested DON also affects intestinal immunoglobulin synthesis. Specifically, DON stimulates intestinal IgA production in mice, leading to an elevated concentration of circulating IgA, increased polymeric : monomeric IgA ratio, and accumulation of IgA in the renal mesangium. The renal damage that occurs following DON ingestion has been characterized as a possible autoimmune phenomenon consequent to the entrapment of circulating IgA immune complexes in the mesangium. 14 IgA nephropathy, which is the most common form of glomerulonephritis in human beings worldwide, affects men 2-5 times more commonly than it affects women. Although the cause of IgA glomerulonephritis is unknown, similarities between the clinical syndrome in human beings and experimental DON intoxication in laboratory animal species (e.g., IgA dysregulation, renal micropathology, evidence that testosterone may be a cofactor in experimental DON-induced IgA glomerulonephritis) suggest that DON may be important in the pathogenesis of IgA glomerulonephritis in human beings. Glomerulonephritis is a common finding at necropsy and represents an important cause of chronic renal failure in horses. Chronic renal failure is comparatively uncommon in horses, and glomerulonephritis is most frequently recognized