Microbial bioconversion studies conducted on the diterpene psiadin have revealed that it was metabolized by Aspergillus niger (NRRL 2295) to give 2alpha-hydroxydeoxopsiadin, Cunninghamella blakesleeana (ATCC 8688a) to give 11beta-hydroxypsiadin, and Cylindrocephalum aureum (ATCC 12720), Gongronella butleri (ATCC 22822), Kloeckera africana (ATCC 20111), and Kluyveromyces marxianus var. lactis (ATCC 2628) to yield 7alpha-hydroxypsiadin. Their structures have been established on the basis of spectral data. The structure and relative stereochemistry of 7alpha-hydroxypsiadin was confirmed by single-crystal X-ray analysis.