Platelet-activating factor, 1 (PAF, 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine), and octadecyl-PAF were synthesized chemically as the racemates. The sn-1-O-alkyl isomers were isolated after treatment of the racemates with phospholipase A2 and subsequent reacetylation of the 1-O-alkyl-2-lyso-sn-glycero-3-phosphocholines released. Analogues of PAF containing unsaturated alkyl moieties at the sn-1 position (2, 4, 5) were synthesized by utilizing the methoxyethoxymethyl protecting group as a novel method for preparing unsaturated alkyl lipids. This procedure provides a facile means for preparing unsaturated either phospholipids of defined structure that may be tritiated to high radiospecific activity for metabolic studies. Unsaturation in the alkyl chain had minimal effect on the bioactivities examined in this study.