Arizonosis occurred in a flock of 10,000 broilers in the state of Sao Paulo. Among 45 specimens submitted for examination at 15 days of age, there was blindness, and nervous symptoms with ataxia, torticollis, and opisthotonos. Necropsy showed caseous material in the vitreous body of the eyeballs and in the cortical region of the brain; S. arizonae 18:z4,z32 (Ar. 7:1,7,8) was isolated. Both ocular and brain lesions were reproduced by exposure of day-old chicks to the isolate by oral and intraocular dosage, by pen contact, and by intraperitoneal injection. Lesions in the brain were most prominent in the ventricles and consisted of necrotic masses containing eosinophilic cells surrounded by macrophages, and epithelioid and multinucleated cells. Lesions of the eye were most often related to the retina.