Plutonic rocks of the Canadian Shield are being assessed as a potential host medium for the storage of radioactive waste. A study of the geological framework of three structural provinces (Superior, Southern, and grenville) within Ontario has resulted in an inventory of 1365 plutons which are identified on Map 1533A at a scale of 1:1,000,000. The plutons have been classified by rock type: granite (sensu lato) comprises 75% of the plutons, gabbro 15%, alkalic rocks 8%, and anorthosite 2%.