T-2 toxin given as a single intravascular dose to swine produced a shock syndrome. Dosages of 0.6 or 4.8 mg/kg were administered to different groups of swine. Shock was characterized by reductions in cardiac output and blood pressure, and increased plasma concentrations of epinephrine, norepinephrine, thromboxane B2, 6-keto PGF1 alpha, and lactate. Total peripheral resistance was unchanged in the high-dose group but decreased in the low-dose group. Pulmonary vascular resistance increased in both groups. Decreases occurred in arterial pH and arterial oxygen partial pressure. No alterations occurred in plasma concentrations of histamine or serotonin.