Abstract The greater part of the enzyme activity producinglongchainaldehydes (LCA) such as (8Z)-heptadecenal, (8Z,11Z)-heptadecadienal, (8Z,11Z,14Z)-heptadecatrienal was found in the 4000 g precipitate of homogenates of the greenalga, Ulvapertusa. The LCA-forming activity was readily solubilized from the precipitate by addition of 0.2% Triton X-100. The solubilized LCA-forming activity showed