Abstract
Mucosal cysts were observed microscopically in the duodenum, jejunum and, to a lesser extent, stomach and large intestine in 102 out of 236 beagle dogs examined. These dogs were used in toxicity studies or had died spontaneously in a breeding colony. The cysts were lined by intestinal epithelium and filled mainly with cellular debris and mucus. Pathogenesis and aetiology of the lesion are unknown.