An elderly man with thymoma, myasthenia gravis, and hypogammaglobulinemia developed profuse watery diarrhea. Infusions of γ-globulin caused the diarrhea to resolve. The patient succumbed to fulminant broncho-pneumonia. At necropsy he was found to have wide-spread cytomegalovirus infection with duodenal and ileal ulceration, subtotal villous atrophy, marked non-specific inflammation of the small intestine and bronchopneumonia. In addition Herpes simplex infection and invasive candidiasis were present. Patients with immunodeficiency are susceptible to a variety of gastrointestinal pathogens, particularly viral.