Dose intensity is emerging as a crucial determinant of success in cytotoxic cancer therapy; however, myelosuppression presents as one of the major complications encountered with increased dose intensity. Therefore, investigators are looking at the use of cytokine administration in combination with cytotoxic therapy to overcome this problem. Interleukin-1 (IL-1) and tumor necrosis factor alpha (TNF-alpha) have been shown to be beneficial in protecting the hematopoietic system from radiation and chemotherapy. In this report, we give an overview of studies using IL-1 and TNF-alpha as protective agents and discuss possible mechanisms involved in their protective action. Mice pretreated with IL-1 and/or TNF-alpha were shown to be protected from the lethal effects of radiation and it has been suggested that the mechanism for this protection may be through the production of the antioxidant enzyme manganese superoxide dismutase. Similarly, aldehyde dehydrogenase, an enzyme important in the metabolic pathway of cyclophosphamide compounds, has been implicated as being important in the protection of hematopoietic cells from 4-hydroperoxycyclophosphamide. While IL-1 and TNF-alpha stimulate both of these enzymes, other mechanisms are probably also operative for other forms of chemotherapy, i.e. IL-1 and TNF-alpha were shown to protect hematopoietic progenitors from phenylketophosphamide, a cyclophosphamide derivative that is not metabolized by the enzyme aldehyde dehydrogenase. Furthermore, malignant as well as normal cells may possess receptors for these cytokines; therefore, IL-1 and TNF-alpha will have to be selective in their protection. They must be capable of protecting normal hematopoietic cells while rendering malignant cells susceptible to the toxic actions of the chemotherapy.(ABSTRACT TRUNCATED AT 250 WORDS)