The in vivo administration of tumor necrosis factor (TNF) provides a new approach to the immunotherapeutic treatment of tumors. We evaluated the pharmacokinetics of murine tumor necrosis factor in mice as a model for application in the human system. TNF had a clearance of 0.013 ml/min/g and a serum half life of 10.5 minutes. Its volume of distribution was consistent with the extracellular space. This information can provide parameters by which to select optimal modes of treatment for eradication of in vivo neoplasms.