the doping is the administration of illicit drugs or other agents in animal competition with the intention of altering its physical performance, whether positive or negative. the aim of this study was to report a case of type i hypersensitivity associated with illicit administration of nandrolone, boldenone and dexamethasone. reference is an equine (thoroughbreds), 5 years old with a history of collapse and sudden death after the administration of medication unknown. samples of blood and urine were recollected for toxicological by competitive elisa. tissue samples were collected by necropsy of lung, liver, kidney, stomach, spleen, heart and central nervous system for histopathological study, the samples were processed by conventional histological methods. the necropsy findings were severe phlebitis right jugular vein, with hematoma in the jugular furrow. severe edema of glottis, pulmonary congestion and hemorrhage. subendocardial petechial hemorrhage. spleen foci of coagulation necrosis. acute hydronephrosis and hematury. liver with accentuated lobular pattern. the rest of the bodies with obvious congestion and hemorrhage. the histological sections showed edema, congestion and severe pulmonary hemorrhage. marked subepicardial hemorrhage. edema and necrosis of splenic subcapsular follicular center. tubular hydropic degeneration, acute tubular necrosis. necrosis of renal cortex. toxicological studies allowed the detection of boldenone, nandrolone and dexamethasone generic in blood and urine samples. in conclusion we report a type i hypersensitivity syndrome associated with the administration nandrolone, boldenone and dexamethasone.