Effective radiotherapy for patients with cancer should include maximal tumor cell killing with minimal injury to normal tissue. However, current radiation doses that can be delivered without causing severe damage to surrounding normal tissues are often insufficient to eradicate a tumor. Recently, a number of agents have been developed to protect normal tissue from the harmful effects of antitumor therapies. The aminothiol amifostine (Ethyol; Alza Pharmaceuticals, Palo Alto, CA/US Bioscience, West Conshohocken, PA) has been the subject of extensive research as a prospective protector. While this drug has been approved for use to reduce toxicities associated with cisplatin, several studies also have demonstrated that amifostine protects normal tissues from both acute and late radiation damage without protecting the tumor. Consequently, higher radiation doses could be used with less than or equal risk to surrounding normal tissues. This report reviews the physicochemical basis of radiation therapy on biologic tissues and the mechanisms responsible for the cytoprotective effects of amifostine. The increasing body of biochemical, preclinical, and clinical data could justify the use of protectors such as amifostine with radiotherapy to provide improved therapeutic efficacy and quality of life for the patient.