Four strains of the heterotrophic marine dinoflagellate, Crypthecodinium cohnii were screened for docosahexaenoic acid (DHA) production potential using shake flask cultures on porphyridium medium containing glucose (5 g l(-1)). Of the four strains tested, C. cohnii ATCC 30 556 had the highest specific growth rate (0.067 h(-1)), the highest biomass concentration (2.046 g l(-1)), the highest growth yield coefficient (0.499 g g(-1)), the highest DHA content (51.12% of total fatty acids and 7.79% of cell dry weight) and the highest DHA yield (159 mg l(-1)). The screening results suggest that C. cohnii ATCC 305 56 is a highly promising microalga for commercial production of DHA.