Abstract. Farmers in the State of Piauí in northeastern Brazil reported nervous signs in ruminants and donkeys after ingestion of Brunfelsia uniflora at the start of the rainy season when the plant is flowering. Leaves of the plant, collected at the start or at the end of the rainy season, were administered in single doses of 5?20 g/kg body weight to 8 sheep and 3 donkeys. Two sheep and 1 donkey that ingested 10 g/kg of the plant in November at the start of the rainy season, when the plant was flowering, developed severe convulsions and diarrhea. One sheep was euthanized and autopsied, and no significant lesions were found. The other sheep and the donkey recovered. Four sheep and one donkey that ingested 10 or 20 g/kg of leaves collected in April, at the end of the rainy season, did not show clinical signs. One donkey that ingested 5 g/kg of leaves collected in November developed diarrhea and recovered. These results demonstrate the toxicity of B. uniflora for livestock and suggest that the plant is toxic at these doses only during the start of the rainy season