When cultured in vitro, peritoneal macrophages, obtained from mice previously inoculated with bacillus Calmette-Guérin, release nitric oxide, which is cytostatic and/or cytolytic for tumor cells. However, it is not known whether nitric oxide has antitumor effects in vivo. Here we demonstrate that nitric oxide is an important mediator of host resistance to syngeneic and xenogeneic ovarian tumor ...