Amifostine (US Bioscience, West Conshohocken, PA; Ethyol, WR-2721), a phosphorylated thiol developed by the United States Army as a protective agent for military personnel in the event of nuclear warfare, has shown protection of normal tissues from the cytotoxic effects of therapeutic radiation and chemotherapy with preservation of cytotoxic effects on the tumor. The basis of this selective protection derives from the relatively rapid uptake and anabolism of Amifostine into normal tissues and minimal, slower uptake into tumor tissue. Preclinical investigations have demonstrated protection of bone marrow stem cells from the toxic effects of radiation and chemotherapy. Several controlled clinical trials demonstrated this hematoprotective effect. In patients given 1.5 g/m2 cyclophosphamide and month later given Amifostine (740 mg/m2) followed by the same dose of cyclophosphamide, the median nadir neutrophil count was significantly increased and duration of neutropenia was significantly reduced by pretreatment with Amifostine. In women with stage III/IV ovarian cancer treated with 1 g/m2 cyclophosphamide and 100 mg/m2 cisplatin +/- Amifostine 910 mg/m2, treatment with Amifostine before cyclophosphamide and cisplatin resulted in a significant decrease in both the incidence and duration of hospital stays for neutropenic fever compared to cyclophosphamide and cisplatin alone. There were equivalent rates of response and duration of survival in both groups. Other studies have shown Amifostine protects bone marrow purged in vitro with 4-hydroperoxycyclophosphamide before autologous bone marrow transplantation. This preservation of marrow stem cells resulted in a statistically significant decrease in time to marrow engraftment, need for platelet transfusions and antibiotics, and duration of hospital stay. Amifostine-mediated protection of normal bone marrow illustrated in preclinical experiments is also evident in clinical trials. Amifostine preserves trilineage stem cells (red blood cells, platelets, and white blood cells) in contrast to the lineage-specific effects of the colony-stimulating factors. Theoretically, Amifostine and the colony-stimulating factors should provide complementary benefits to bone marrow recovery and function after cytotoxic therapies. These observations offer the promise of using high doses of chemotherapy to exploit antitumor, dose-response relationships in clinical trials.