The Authors describe the clinical features observed in a herd of dairy cows during an acute poisoning caused by endosulfan. Neurological signs, mainly characterised by mydriasis, sialorrhea, tremors, ataxia and aggression rapidly appeared after the ingestion of maize silage contaminated by this organochlorine. Five animals died in a few hours, after showing dyspnea and clinical signs of pulmonary oedema. A poisoning was suspected on the basis of the clinical signs and their evolution as well as the hystopathologic findings; diagnosis was made by demonstrating endosulfan in maize silage and in ruminal contents obtained from died cows