The present invention relates to methods for the conversion of the substrate specificity of desaturases. Specifically, the present invention pertains to a method for the conversion of the substrate specificity of a Δ5 and/or Δ6 desaturase to the substrate specificity of a Δ4 desaturase, the method comprising: identifying regions and/or amino acid residues which control the substrate specificity of (i) the Δ5 and/or Δ6 desaturase and (ii) the Δ4 desaturase; and replacing in the amino acid sequence of the mentioned Δ5 and/or Δ6 desaturase, the regions and/or amino acid residues which control the substrate specificity of the Δ5 and/or Δ6 desaturase, by the corresponding regions and/or amino acid residues which control the substrate specificity of the Δ4 desaturase, thereby converting the substrate specificity of the Δ5 and/or Δ6 desaturase to the substrate specificity of the Δ4 desaturase. The present invention further concerns a method for the conversion of the substrate specificity of a Δ4 desaturase to the substrate specificity of a Δ5 and/or Δ6 desaturase, the method comprising: identifying regions and/or amino acid residues which control the substrate specificity of (i) the Δ4 desaturase and (ii) the Δ5 and/or Δ6 desaturase; and replacing in the amino acid sequence of the indicated Δ4 desaturase, the regions and/or amino acid residues which control the substrate specificity of the Δ4 desaturase, by the corresponding regions and/or amino acid residues which control the substrate specificity of the Δ5 and/or Δ6 desaturase, thereby converting the substrate specificity of the Δ4 desaturase to the substrate specificity of the Δ5 and/or Δ6 desaturase. In addition, the invention encompasses desaturases with converted substrate specificity.