Ultrasonography was used to evaluate the duodenum of 6 clinically normal horses. Examinations were performed in horses which each, alternatively, received diets of; 1) concentrates and hay, 2) hay only, or 3) after 36 hours of starvation. The duodenum was constantly visualized just ventral to the right kidney at the 16th and 17th intercostal spaces on a line joining the olecranon and tuber sacrale. Cranial to the 16th intercostal space visibility depended on thickness of interposing liver and lung field interference. Duodenal distensions, contractions and content are described. Starved horses had fewer contractions and distensions than horses on hay, or hay and concentrate diets but the difference was not significant. Duodenal wall thickness ranged from 3–4 mm. Ultrasonographically five layers, corresponding to the mucosal surface, mucosa, submucosa, muscularis propria and serosa, could be identified. A necropsy specimen of the duodenum was evaluated histologically and Ultrasonographically in a water bath for compariso