The isolation and structural identification of the minor components of cod liver oil was undertaken with particular attention to those of novel structure. A series of procedures based on urea crystallisation, argentation chromatography and preparative glc were developed for the isolation of the unusual acids present at low level. With these procedures, phytol-based acids (isoprenoids), furanoid acids and a series of mono-and diunsaturated branched-chain fatty acids were isolated. These fatty acids were characterised by a combination of mass spectrometry and nmr. In the case of the branched-chain acids, a GC-MS capillary system was used. Pyrrolidide and O-TMS derivatives of the acids were also studies for the location of double bonds. Three phytol-based acids were identified. In addition to confirming the presence of nine furanoid acids, new furanoid acids were also discovered. The discovery of a branched diunsaturated acid is significant. The 7,9 dimethylhexadec -6,8-dienoic acid is novel and is reported in this study for the first time. In addition to these acids, the major component acids of cod liver oil were isolated and identified. For the isolation of these, procedures such as low temperature crystallisation, argentation chromatography and preparative glc were adopted. Ozonolysis followed by reduction with triphenylphosphine was used for the analysis of the positional isomers of monoene acids. For diene acids ozonolysis was followed by reduction with sodium borohydride. The merits and demerits of these two procedures for the location of double bonds in a fatty acid chain are discussed. Oxymercuration-demercuration was used for the characterisation of some of the polyene acids. Only polyene acids having △3t, △4 or △5 unsaturation react in this procedure to furnish cyclic ethers which can be isolated and identified. The fragmentation characteristics of these cyclic ethers are discussed.