The present invention relates to a method for the production of unsaturated fatty acids with at least two double bonds. The invention further relates to the use of the nucleic acid sequence of SEQ ID NO: 1 encoding a polypeptide having delta-5 desaturase activity in the method and for generating a transgenic organism, preferably a transgenic plant or microorganism with an increased content of fatty acids, oil or lipids with unsaturated long chain fatty acids, to their homologs or derivatives, and to gene constructs encompassing these genes. The invention also relates to the use of the nucleic acid sequences alone or in combination with further desaturases and/or elongase genes in the method and for generating transgenic organisms.