One outbreak of sudden death occurred in the Agreste region of Paraiba, Brazil in a herd of 129 cattle. When the herd was driven from the area, 40 cattle had clinical signs characterized by instability, staggering and lying down or falling. Twenty cattle died and the other 20 recovered. Dry Mascagnia rigida collected in the paddockwas administrated to 3 groups of 2 rabbits each at doses of 1.25, 2.5 or 5 g/kg bw. All rabbits ingesting 2.5 and 5 g/kg bw died acutely between 3 h 25 min and 16h 15 min after dosing. M rigida collected in another farm where the disease was not observed was given to 3 groups of 2 rabbits each at doses of 5, 10 or 20 g/kg bw. Only I rabbit died suddenly 3 h and 25 min after ingestion of 20 g/kg bw. These results tend to support M rigida as a cause of sudden death in cattle and rabbits They also demonstrate variations in the toxicity of the plant, which seems reflective of the variation in disease occurrence in different areas where it occurs.