A study was made of the heavy minerals from the glacial and interglacial deposits of Pleistocene age exposed in the Don Valley, Toronto, Ontario. The mineral occurrences are listed and special characteristics noted. The actual mineral occurrences are very similar in glacial and interglacial beds but when the relative abundance of certain minerals is plotted as percentage of total heavy minerals present, curves are obtained showing a rather sharp difference between glacial and interglacial beds and a very close resemblance between the various interglacial beds examined. In all cases the mineral assemblage is of typically Pre-Cambrian derivation. It is thought that the materials of the interglacial beds were derived, either from the glaciers and icebergs themselves, or from older boulder clays, and very little from the Paleozoic sediments which underlie the region.