The uropygial gland fats from the razorbill, guillemot (two varieties) and the black guillemot arc very complex mixtures of ester waxes. Among the wax acids n- octanoic acid dominates followed by homologous series of 2-, 4- and 6-monomethyl-, 2,6-, 2,8-, 2,10-, 4,6-, 4,8-, 4,10-, 4,12-dimethyl- and 2,4,8-, 2,6,10-, 2,6,12-, 4,6,10- and 4,8,12-trimethyl-substituted fatty acids. The alcoholic components consist of n-, 2-, 4-, 6-, 8- and 12-monomethyl- as well as 2,6-, 2,8-, 2,10-, 4,6-, 4,8-, 4,10- and 4,12-dimethyl - branched alkanols. The black guillemot differs from the other species investigated by the occurence of fatty acids which have the first branch in 2- while the others start with the 4-position. The chemotaxonomy of the 20th order of the natural system is discussed.