PURPOSE: To obtain a heavy hydrogen labeled higher fatty acid labeled with a stable isotope, applicable for metabolic experiments and measurement of metabolic ability of a wide range including in vivo of human body of eicosapentaenoic acid having pharmacologic action such as inhibitory action on blood platelet aggregation.

CONSTITUTION: Heavy hydrogen labeled eicosapentaenoic acid, a heavy hydrogen labeled eicosatetraenoic acid or their esters. These compounds are efficiently produced by culturing an eicosapentaenoic acid producing bacterium such as Schwanella putrefaciens (FERM-BP-1,625), Alteromonas putrefaciens (FERM- BP-1,624) or Pseudomonas putrefaciens (FERM-BP-1,623) as an eicosapentaenoic acid producing marine bacterium in a medium using heavy water instead of light water. The content of heavy hydrogen in the produced compound rises with increase in heavy hydrogen in the medium and further rises by addition of heavy hydrogen labeled sodium acetate to the medium.