A method of producing DHA for use in introduction into human or animal bodies comprising treating Isochrysis with nitrogen in the form of a nitrate at a concentration between 10 mg and 50 mg NO3-N/L and at a temperature under 40 DEG C and over 13 DEG C. The DHA can be extracted by means such as solvent extraction using, for example, heptane, followed by gas liquid chromatography. <IMAGE>
