Acute intoxication by seeding Crotalaria retusa occurred during the dry season, in a flock of 80 sheep, in the semi-arid region of the state of Paraiba, northeastern Brazil. Anorexia, severe depression, mild jaundice, incoordination and recumbence were observed in 16 sheep that died within 12 h. At necropsy the liver had a nutmeg appearance. Seeds of C. retusa were found in large amounts in the rumen of the dead animals. Histologic lesions of the liver were characterized by centrilobular necrosis. Seeds of C. retusa were given to six sheep at doses of 2.5 (two sheep), 5, 10, 20 and 40 g/kg bw (one sheep for each dose). Sheep ingesting 5-40 g/kg bw were killed when moribund, 38-120 h after the start of the administration. Clinical signs and gross and histologic lesions were similar to those observed in field outbreak. The seeds used in the experiment contained 1.4% of monocrotaline. It is concluded that hungry sheep can be affected spontaneously by acute monocrotaline intoxication when they ingest large amounts of C. retusa seeds in a short period of time.