THE SIGNIFICANCE of the genetic and environmental factors in the incidence of nonspecific inflammatory disease of the bowel continues to stimulate great interest. Studies of multiple occurrences in family units have been published.1-5Theories as to such occurrences, ranging from a common immunologic defect within a family to an environmental factor such as early weaning, have been proposed. Finding multiple cases of granulomatous enteritis within a family unit is probably more than a casual coincidence. The reported prevalence of regional enteritis in England varies from 9 per 100,000 to 14 per 100,000. Figures obtained in the United States are slightly higher.5 The authors have had the opportunity of studying a family group consisting of the parents and two siblings, a son and a daughter. Only the mother escaped the presence of incapacitating regional enteritis. With an assumed prevalence in the United States of 20 per 100,000,6the