Twenty horses died 30 d after being fed a diet containing 40% of tritured Crotalaria juncea seeds. Before death, they had staggering, dyspnea and fever. At necropsy the most evident lesions were areas of lung parenchyma consolidation and enlarged and congested livers. Histopathological examination revealed diffuse fibrosing alveolitis with hyaline membranes, suggesting a blood-borne insult, and passive congestion in the liver with compression of the hepatocyte trabecules. To confirm the diagnosis, guinea pigs were given 60% of a commercial diet + 40% tritured C juncea seeds. After 4 mo of feeding the animals died with dyspnea. Their lungs had diffuse fibrosing alveolitis with discrete formation of hyaline membranes and the livers were congested. Reproduction of the lesions implicated the plant and supported the diagnosis of C juncea intoxication in the horses.