Screening of several filamentous fungi for hydroxylation of cis-bicyclo[3.3.0]octane-3,7-dione showed only reduction of the keto groups. Several ways to protect the keto groups have been tested. This related in hydrolysis with subsequent reduction, or rejection of the substrate. Only when 2,2-dimethyl-1,3-propanediol was used to form diketals, the substrate was relatively stable and at least one hydroxylated product could be detected.