Enzymatic systems in human blood cells are described for the activation and inactivation of a biologically active phospholipid (1-alkyl-2-acetyl-sn-glycero-3-phosphocholine) with hypotensive, platelet-aggregating, and inflammatory properties. The results document the presence of alkyldihydroxyacetone-phosphate synthase (forms the O-alkyl linkage in lipids), 1-alkyl-2-lyso-sn-glycero-3-phosphocholine: acetyl-CoA acetyltransferase (produces the biologically active molecule), and 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine: acetylhydrolase (destroys the biological activity) in human neutrophils and eosinophils. Both the acetyltransferase and acetylhydrolase activities are increased severalfold after treatment of normal neutrophils with ionophore A23187; however, alkyldihydroxyacetone-phosphate synthase activity is not influenced by the ionophore. Eosinophils isolated from patients with eosinophilia have significantly greater activities of all the enzymes studied than the eosinophils isolated from normal individuals. Our results indicate the acetyltransferase responsible for 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine synthesis may serve an important role in human blood cells that release this biologically active phospholipid. Moreover, the acetyltransferase activity was found to be dramatically influenced by calcium flux.