We studied the effect of OK-432 combined AIT in 24 cases of liver metastases of breast cancer. Eleven of the 16 patients (69%) who received intraarterial transfer responded to this therapy. On the other hand, no patients responded to intravenous or intraportal transfer. The minimum cell number for a therapeutic response was 10(9) cells. Four patients had abscopal effects after therapy. The serum CEA level paralleled the therapeutic effects. There were no severe side effects accompanying this therapy. These results indicate that intra-arterial OK-432 combined AIT should be the first choice therapy against liver metastases of breast cancer.