Intratumoral administration of a large dose of OK-432 has two antitumor functions; a direct cytotoxic effect and an indirect effect through the host reticuloendotherial functions. It has been pointed out that this method, however, occasionally results in shock. Several investigators have suggested the importance of the use of general anesthesia to avoid such shock. In order to explore the hemodynamic effect of intratumoral injection of OK-432, a simulated experiment (OK-432 or saline intramuscular injection) was carried out utilizing 10 anesthetized and 10 unanesthetized dogs. In addition, hemodynamic alterations during the OK-432 administration were studied in nine patients under neuroleptal anesthesia. In both anesthetized and unanesthetized dogs, OK-432 intramuscular injection resulted in a slight decrease of the mean arterial pressure, left ventricular systolic pressure and cardiac output as compared with those of the saline injected dogs. The hemodynamic alterations, however, were minimal and were thought not to cause severe hemodynamic derangements. Clinical experiences also showed no serious hemodynamic effects by the OK-432 intratumoral injections. It was concluded that the OK-432 intratumoral injection appeared not to induce hemodynamic derangement when applied to euvolemic and hemodynamically stable patients.