FOLLOWING the suggestion of Dewar1, it is now generally accepted that the mould metabolic products, stipitatic acid, puberulic acid and puberulonic acid are derivatives of tropolone2. Erdtman and Gripenberg3 have shown that α-, β- and γ-thujaplicins from Thuja plicata, the western red cedar tree, are, respectively, α-, β- and γ-isopropyltropolones. γ-Thujaplicin was found to possess fungicidal activity; when spores of Pullularia pullulans were suspended in a 0.02 per cent solution, 100 per cent survived after 1 hr., 11 per cent after 3 hr. and none after 6 hr. and 24 hr. exposure. Two of us (J. W. C. and A. R. S.) have recently described a synthesis of 3 : 4-benztropolone4.