Resin particles (diameter 45-75 microns) were labelled with 90Y, suspended in a glucose/dextran solution and infused into the kidneys of 3-month-old pigs (tumour model). Both kidneys of each animal were embolized with particles, but only one with active (90Y loaded) particles and the other, for comparison, with inactive particles. The organ measurements showed less than 1% of injected activity in bone, bone marrow, liver and lung compared to greater than 99% retention by the kidneys. Only minimal shunted activity was found in blood (less than 0.27%) and urine (less than 0.07%). There was a clear shrinkage of the 90Y-treated kidneys with a reduction in weight of up to 50%. Histologically, the ischaemic lesions (infarcts and atrophy) were clearly more pronounced and extensive in the 90Y-embolized kidneys than in the non-radioactive embolized kidneys. Furthermore, severe arterial wall changes and fibrotic necrosis due to radiation damage were observed in the 90Y-treated kidneys. It is concluded that with intra-arterially applied particles a dose of about 100 Gy is sufficient to completely destroy tissue-specific structures. Complications due to acute necrosis or inflammatory reactions were not observed, and there were no shunt related alterations seen in the liver or lungs. The 90Y-loaded resin particles are considered suitable for a super selective intra-arterial radioembolization.