The authors have investigated the effect of OK-432 on the spontaneous metastasis from a murine fibrosarcoma, either an NFSA or a SANH, that had been transplanted into the right thigh of C3H mice. When the NFSA or the SANH tumors grew to 7 mm in diameter, they were irradiated with a single dose of 30 Gy and 20 Gy, respectively. A local administration of OK-432 (2.5 KE) around each of the tumors was initiated immediately after irradiation and continued twice a week. It was found that regrowth in both tumors was not modified by the OK-432, though the mean number of metastatic lung nodules per mouse from either tumor was significantly decreased. The incidence of a lung metastasis also was reduced by the OK-432 but not significantly. Further, mice that had received a SANH tumor transplant developed a lymph node metastasis in the abdominal cavity that was depressed by the OK-432.