The strong tumor-selective cytocidal action of tumor necrosis factor (TNF) has been observed in vitro and in vivo. Sato et al. have reported that it was possible to induce a primed state of TNF triggering by injection of purified protein derivative (PPD) even a long time after BCG sensitization, suggesting that this treatment could be applied to human patients. In the present study, we achieved a partial response of a metastatic lesion in a patient with renal cancer by the induction of endogenous TNF by PPD and OK-432 (a streptococcal preparation). This study suggested the possible application of this therapy to also patients with malignant tumor which are highly resistant to any conventional antitumor therapy.