Twenty-five moss species were screened for the presence of arachidonic and eicosapentaenoic acids. Six species belonging to the families Brachytheciaceae and Hypnaceae contained the highest levels of these polyunsaturated fatty acids. Leafy gametophytes contained 24-37% arachidonic acid and 9-23% eicosapentaenoic acid, whereas protonema cells cultured axenically at 20° contained 20-42% and 2-5% of the two acids, respectively, when calculated as the percentage of total fatty acids in the lipid fraction. The total moss lipids were represented by ca 50% neutral lipids, 20% phospholipids and 30% glycolipids. The latter fraction was particularly rich in arachidonic and eicosapentaenoic acids. The total lipid content could be induced from 5% up to 20% of dry weight in cultured protonema cells. © 1990.