The present invention relates to methods of synthesizing long-chainpolyunsaturated fatty acids, especially eicosapentaenoic acid,docosapentaenoic acid and docosahexaenoic acid, in recombinant cells such asyeast or plant cells. Also provided are recombinant cells or plants whichproduce long-chain polyunsaturated fatty acids. Furthermore, the presentinvention relates to a group of new enzymes which possess desatorase orelongase activity that can be used in methods of synthesizing long-chainpolyunsaturated fatty acids.