This article reviews the prevention of oral and systemic infection in bone marrow transplantation and radiation patients. Prophylaxis of herpes virus reactivation in bone marrow transplant and leukemic patients has resulted in reduced morbidity associated with their medical management. In order to reduce the risk of systemic infection, reduction in ulcerative mucositis is desirable. The use of antifungal and antibacterial agents has not been encouraging to date. Cytoprotective agents have shown some initial success in preventing mucosal breakdown. Further study is required to confirm these initial results.