Abstract From the organic extract of a deep-water Hawaiian sponge Dactylospongia sp., a new potent antioxidant and antimicrobial meroterpenoid, puupehenol (1), was isolated. The structure of 1 was determined using spectroscopic techniques (1H and 13C NMR, MS, IR, UV, [α]D). The known compound puupehenone (2) was also isolated and suggested as a probable artifact of the isolation procedures. Complete unambiguous 1H and 13C NMR data are provided for compounds 1 and 2. Bioassays performed with 1 and 2 showed them both to be very effective antioxidants and to have antimicrobial properties.