P1-Dolichyl P2-ALPHA-D-mannopyranosyl pyrophosphate (9) has been chemically synthesized by a method developed for the corresponding citronellyl derivative, which also contains a saturated alpha isoprene residue. In each case, the P1-polyisoprenyl P2-diphenyl pyrophosphate was treated with 2,3,4,6-tetra-O-acetyl-alpha-D-mannopyranosyl phosphate to give a fully acetylated pyrophosphate diester, which was purified chromatographically and subsequently deacetylated. The citronellyl and dolichyl pyrophosphate diesters were compared with the previously synthesized citronellyl and dolichyl alpha-D-mannopyranosyl phosphate, respectively, by chromatography and by hydrolysis experiments. Good separations of the monophosphate from the corresponding pyrophosphate were achieved by silica gel tlc in a variety of solvent systems. Brief dilute acid hydrolysis of both the mono- and pyrophosphate diesters gave D-mannose and no alpha-D-mannosyl phosphate, the other products being polyprenyl phosphate and pyrophosphate, respectively. When the polyprenyl alpha-D-mannopyranosyl mono- and pyrophosphate diesters were treated with hot dilute alkali, the major products were polyprenyl phosphate and substances arising from the breakdown of D-mannose, indicating that the alpha-D-mannosyl phosphate bond was the most labile linkage in both compounds. However, the formation of a small proportion of free dolichol indicated that alpha-D-mannosyl phosphate was also formed to a minor extent. The interpretation of the results of the alkaline hydrolysis was complicated by the instability of D-mannose under basic conditions, it being almost completely degraded by even a brief treatment.