The objective of the study reported here was to document the distribution of epidermal growth factor receptor (EGFr) and quantitate receptor density in normal as well as ulcerated equine gastric squamous mucosa. Fifteen horses with endoscopically normal stomachs were divided into three equal groups. Group 1 was a normal control. A protocol that alternated 24 hour periods of free-choice hay with 24 hours of feed deprivation was utilized to induce squamous mucosal gastric ulceration in Group 2 (48 hours total off-feed) and Group 3 (96 hours total off-feed). Gastric tissue was collected from 3 stomach locations at post-mortem examination and an avidin-biotin immunoperoxidase technique was developed to stain the formalin-fixed tissue for EGFr. A computerized image analysis system was used to measure EGFr area and mean intensity values at four sites within the epithelium from the basal cell layers to the lumen in the ulcer/erosion margin, erosion bed, and 10-14 mm distant from the lesion. / Master of Science