Nondegradable glass microspheres (35 mu) were injected into the portal vein for toxicity test in 15 rabbits. In 10 animals the microspheres were loaded with 90Y, giving liver absorbed doses between 24.6 and 437.4 Gy, and in 5 with 89Y (control group). The total amount of microspheres injected in each animal varied between 35 and 140 mg. The rabbits in the experimental group tolerated the effect of radioembolization in a dose 4 times higher than the upper limit of the clinical dose (100 Gy). After injection of 90Y glass microspheres into the portal vein of rats with diethylnitrosamine (DEN)-induced hepatic carcinoma, the microspheres, in addition to the liver parenchyma, accumulated in central and peripheral parts of the cancer nodules, causing necrosis. The internal radiation therapy of 90Y glass microspheres delivered via the portal vein may be an effective nonsurgical method for the treatment of liver cancer, especially in small nodules.