Interleukin-1 alpha (IL-1 alpha) has potent effects on hematopoiesis and can significantly enhance the anti-tumor activity of cytotoxic drugs. Studies were undertaken here to determine whether IL-1 alpha, administered by continuous infusion, could prevent carboplatin (CBDCA)-mediated thrombocytopenia and enhance CBDCA-mediated anti-tumor effects. RIF-1 tumor bearing mice were treated with CBDCA and IL-1 alpha either by a single bolus injection or by continuous infusion through the use of ALZET pumps. The duration and extent of CBDCA-induced thrombocytopenia in tumor-bearing mice was diminished when IL-1 alpha was administered continuously as compared to CBDCA alone or CBDCA plus a single bolus injection of IL-1 alpha. In addition, IL-1 alpha induced potentiation of CBDCA anti-tumor activity in vivo was significantly increased when IL-1 alpha was administered by continuous infusion. These results demonstrate the potential efficacy of IL-1 alpha by continuous infusion.