Microcapsules, 106 micron (range, 50-350 micron), of different capsular materials (monoglyceride, monodiglyceride, natural wax, cellulose polymer, or lactic acid polymer) with and without floxuridine (2'-deoxy-5-fluorouridine, FUDR) were intraarterially injected into dog kidneys. The drug-release characteristics of the microcapsules, as determined by analysis of renal and systemic venous blood samples over a 6-hour period, were uniphasic or multiphasic depending on the capsular material. Histologic changes of varying degrees were noted in all kidneys embolized except for those subjected to capsules of the cellulose polymer. The most striking changes were produced by the lactide polymer capsules. The potential applications of microencapsuled chemotherapeutic agents in intraarterial transcatheter treatment of cancer are discussed.