High resolution gas chromatographic analysis of natural 2,6,10,14-tetramethylpentadecane from shark lipids shows it to comprise only the 6(R),10(S)-meso-isomer. This was confirmed by gas chromatographic analysis of esters of the acidic products of dichromate oxidation. These data support the hypothesis that the alkane derives from zooplanktonic metabolism of phytol (trans-3,7(R),11 (R),15-tetramethylhexadec-2-en-1-ol).