Phosphates of all-Z- and 3-demethyl-tri-trans, di-cis-hexaprenols have been prepared and studied as substrates for enzymes of the Salmonella anatum O-specific polysaccharide biosynthesis. Methyl group in alpha-isoprenic unit proved to be essential for the enzyme-substrate interaction, whereas the presence of E-isoprenic units near the omega-end of the polyprenol is not significant.