The lipids of marine organisms are characterised by the presence of polyenoic fatty acids containing 16 to 22 carbon atoms with 2 to 6 conjugated double (ethene) bonds which originate from unicellular marine phytoplankton. Of particular interest, because of their essential benefits to human nutrition and health, are the long chain polyunsaturated fatty acids, eicosapentaenoic acid (EPA), which has 20 carbon atoms in the chain and 5 double bonds (denoted 20:5), and docosahexaenoic acid (22:6) or (DHA). The double bonds have the cis configuration which confers greater instability and lower melting point than the trans configuration. Thus, the correct chemical notation is cis-5,8,11,14,17-eicosapentaenoic acid and cis-4,7,10,13,16,19- docosahexaenoic acid. These acids are usually the major PUFA constituents of fish lipids and fish oils, and belong to the n-3 (w-3) series in which the first double bond is at the third carbon atom along the chain from the terminal methyl group. They are considered to be important inter alia in relation to cardiovascular disease, inflammatory diseases and cancer, and DHA is important for normal post-natal development of cerebral and visual tissues. There is a wide range of fish oil supplements available for retail sale containing approximately 12% DHA and 18% EPA. Also see w(omega)-3 fatty acids.