Eucalyptus sideroxylon leaves collected throughout the habitat of this tree were of two classes. The polyphenol aglycones in the leaves collected from different samples of the normal form of the tree were very similar in nature and amount but the composition of the glycosides was generally characteristic of a geographical region. The latter compounds included the 3-glucoside, 3-rhamnoside, 3-rutinoside of quercetin, the 3-rhamnoside and 3-rutinoside of kaempferol; catechin, epicatechin, shikimic, chlorogenic and p-coumarylquinic acids and some unidentified products were also present. Leaves of the second class were characterized by large amounts of stilbenes, chlorogenic and p-coumarylquinic acids and in some cases dihydrokaempferol 3-rhamnoside; several of the polyphenols in the first class were also present. The leaves of the second class were collected from trees recognized as variant forms and in two areas trees of both forms have been found growing close together. Both forms contain leucocyanidin and esters of gallic, ellagic and gentisic acids. A new flavone, 5,4'-dihydroxy-7-methoxy-6,8-dimethylflavone was isolated from a variant sample and the 4'-methoxy derivative was detected in both forms. The wood extractives of both forms were identical and contained resveratrol and another hydroxystilbene and their glucosides. While the composition of the flavonoids in the leaves of different variant forms remains relatively constant the major stilbene in leaves of the second class varies; it can be the 3-glucoside of either 3,4',5-trihydroxy-, or 3,3',5-trihydroxy-4'-methoxy- or another hydroxy-stilbene.