The authors give the histories of four patients with collections of air under the mucosa or serosa of the intestinal tract and its peritoneal attachment. The 4 are representative of 16 patients, observed by the authors, with pneumatosis cystoides intestinalis and a common history of allergic difficulties and asthma. The etiology of the disease has been the subject of many theories, but a complete understanding of the pathogenesis has not yet been attained. The two dominant concepts at present are based on (1) a mechanical theory which assumes that the gas is forced through a fissure in the intestinal mucous membrane and (2) a chemical theory which assumes that gas is produced by fermentation and absorbed by the mucous membrane. Investigation for the existence of a cause-and-effect relationship between allergy or asthma and air in the intestinal wall is suggested as a worthy endeavor.