Fatty acids of twelve species of cyanobacteria grown under different photoautotrophic conditions were studied and their composition was compared with literature data of many other species. We have come to the conclusion that the lipids of cyanobacteria do not contain fatty acids with a chain longer than 18 carbon atoms. In our opinion, omission of an analytical procedure, i.e. purification of fatty acid methyl esters before gas chromatography, leads to incorrect interpretation of the results. Absence or presence of fatty acids was suggested as a useful taxonomic marker and a proper diagnostic indicator in the commercial application of cyanobacterial biomass.