The patients having bone metastases from prostatic and renal cancer, of whom 4 were resistant to prior radiotherapy, hormone therapy and/or chemotherapy, were subjected to arterial chemoembolization with mitomycin C microcapsules. In these patients, 12 metastatic lesions in the pelvic bone (5), lumbar spine (3), scapula (1) and rib (1) were treated. The mean size of the target lesions was 41.5 cm2 (range, 6-143). The mean number of microcapsule infusion into the tumor supplying arteries was 2.6 (1 to 10) and the mean interval of repeat infusion in 6 patients was 6.4 months (0.5 to 28). A complete remission of pain was obtained in 9 (75%) of the 12 evaluable lesions and a partial remission in 3 (25%). Motor disturbances were remarkably improved in all of the evaluable 6 lesions. Objective tumor response such as recalcification and reduction of size or vascularity was found in 9 (75%) of the evaluable 12 lesions. These effects were maintained for the mean follow-up period of 17.1 months (3 to 48). The results will indicate that this therapy can be used as an effective measure in the treatment of metastatic bone tumors.