The gross and microscopic changes in swine following a single intravascular (iv) dose of T-2 toxin are described and evaluated quantitatively. T-2 toxin, in 70% ethanol, was given iv at 0 (5 pigs), 0.6 (5 pigs), 1.2 (1 pig), 4.8 (5 pigs), or 5.4 (2 pigs) mg/kg to 40 to 60 kg female crossbred pigs. The 4.8 and 5.4 mg/kg group pigs died between 5 and 10.5 hr after treatment, while the 0, 0.6, and 1.2 mg/kg pigs were killed at 24, 24, and 12 hrs after treatment, respectively. Morphologic examination was performed at the gross and light microscopic levels. In addition, a quantitative evaluation of microscopic changes present in lymphoid tissues and intestinal tract was performed using a semiquantitative scoring system. Gross lesions in the T-2-treated pigs consisted of edema, congestion, and hemorrhage of the lymph nodes and pancreas; congestion and hemorrhage of the gastrointestinal mucosa, subendocardium, adrenal gland, and meninges; and edema of the gall bladder. Histologic examination confirmed the gross observations. Additional microscopic lesions included widespread degeneration and necrosis of the lymphoid tissues as well as of the surface and crypt epithelium of the gastrointestinal mucosa; mild scattered necrosis of pancreatic acinar cells, myocardium, bone marrow cells, adrenal cortical cells, and tubular epithelium of renal medulla; and mild interstitial pneumonia. A dose-dependent increase in lesion severity was observed except for the pancreatic lesion which was slightly more apparent in the pigs from the 0.6 mg/kg group. These findings indicate that T-2 toxin-induced lesions in the lymphoid tissues and gastrointestinal tract of pigs are similar to those of other species the pancreas and heart should be considered as additional target organs in the pig, and both rapidly dividing cells and those with little or no turnover are damaged by T-2 toxin.