Tigaso oil, which is obtained as an exudate from a tree of the Anacardiaceae family identified as Campnosperma sp. vel. aff. C. brevipetiolata Volk., has been found to contain an optically active compound. This is considered to be (+)-5-hydroxy-5-(nonadec- 10'-en-2'-onyl)cyclohex-2-enone (V), a new type of natural product. It is very closely related to the phenol, campnospermonol (I ; R=H) which is the major component of Tigaso oil, and is readily converted into a mixture of campnospermonol and campnospermonyl alkyl ether by heating in alcoholic hydrochloric acid. On pyrolysis, V yields resorcinol and methyl oleyl ketone almost quantitatively. ($)-3-Hydroxy-3-(nonadecan-2'-ony1)cyclohexanone (VI) obtained by catalytic hydrogenation of V is easily dehydrated to 3-(nonadecan-2'-onyl)cyclohex-2-enone (VII) which has acidic properties and gives a yellow solution in alkali. Heating VII in alkali gives stearic acid and 3-methylcyclohex-2-enone as the principal products. When the hydroxydiketone (VI) is heated the major reaction is dehydration to give VII, but pyrolysis also takes place, giving methyl stearyl ketone and dihydroresorcinol. 3-(Nonadecan-2'-ony1)cyclohexanone (VIII) is obtained by catalytic hydrogenation of VII and also by oxidation of the diol X, itself prepared from hydrocampnospermonol (II ; R =H) by high pressure hydrogenation. The structure originally assigned to campnospermonol by Jones has been established by the synthesis of hydrocampnospermonyl methyl ether, from 3-methoxyphenylacetyl chloride and diheptadecyl cadmium. The odour of Tigaso oil is partly due to a small amount of a volatile ketone C7H12O which consists mainly of 3-methylcyclohexanone ; probably a mixture of (+)- and (-)-isomers with the (-)-isomer preponderant.