Microbial degradation of phytol is often proposed to be the primary source of the acyclic isoprenoid acids observed in sediments, yet only a limited number of these acids have been found in bacterial cultures grown on phytol. This study reports detailed capillary gas chromatography and gas chromatography-mass spectrometry analyses of the products resulting from growth of marine bacteria on phytol as the sole carbon source. We examined two strains of bacteria which were able to oxidize phytol to phytenic acid but were unable to further degrade phytol. The third isolate studied converted phytol to a mixture of five saturated isoprenoid acids. The C17 isoprenoid acid produced was of particular interest, since its genesis from phytol would have involved several unusual intermediates. It is suggested that this acid is produced by bacterial metabolism of the C18 isoprenoid ketone (produced from phytol abiologically under oxic conditions) and that its abundance is thus a sensitive indicator of sedimentary depositional conditions.