The use ofChaetomium cochlioidesandDiplodia gossypinato perform biotransformations of bicyclic and tricyclic sesquiterpenoids was examined. Using humulene as a substrate, a strain ofChaetomium cochlioideswas found to produce numerous epoxides and hydroxylated derivatives. Hydroxylation of humulene monoepoxide proceeded much more readily than hydroxylation of the hydrocarbon. A further strainof Chaetomium cochlioideswas found to be enantioselective with respect to its products of biotransformation. Similar epoxidation and hydroxylation biotransformations were performed on caryophyllene with the same fungal strain. The use of a strain ofDiplodia gossypinato oxidize calarene and globulol also was studied. Many of the biotransformations studied were found to produce reasonable yields. Also, oxygenated sesquiterpenes were found to be more readily biotransformable than hydrocarbons. This was thought to be because of their better solubility in water.