In the heterocysts of nitrogen-fixing cyanobacteria structurally unique glycolipids are contained, organized in a laminated layer which protects the enzyme nitrogenase by inactivation from oxygen. The glycolipids have been investigated in representatives of all families able to form heterocysts and it has been found that their structures consists of glycosides of long chain triols, tetrols and hydroxyketones. The sugar moiety is mainly α-glucose, but α-galactosides, α-mannosides and a β-glucoside have also been found. Biosynthetic studies have shown that the aglycones originate from acetate, presumably through the polyketide pathway. Two chemical synthesis of the most widespread of the heterocyst glycolipids have been reported until now.