Hematotoxicity is caused by a number of agents such as a benzene by-product called hydroquinone and the antitumor agent doxorubicin. This is a basic research study, conducted using normal human donors, of mechanisms involved in hematotoxicity and of the protective response of human hematopoietic progenitor cells to hematotoxic agents. Tumor necrosis factor exposure protects these cells from a subsequent exposure to hematotoxic agents. The alteration of gene expression in these cells caused by tumor necrosis factor is being studied. Additionally, the tumor necrosis factor-induced biochemical pathways involved in protection of human hematopoietic progenitor cells will be studied.