The transfer of radioactivity from cytidine-5'-diphosphate ethanolamine into 1-alkyl-2-acyl-sn-glycerophosphorylethanolamine of neuronal and glial cells from adult rabbit brain cortex has been investigated in vitro. The synthesis of 1-alkyl-2-acyl-sn-glycerophosphorylethanolamine in both cell populations was stimulated 23-25-fold by the addition of 6 mM alkylacylglycerol. The neuronal cell-enriched fraction was found to possess/unit protein a 1.7-1.8-fold ethanolaminephosphotransferase activity (EC 2.7.8.1), as compared to the glial fraction, when saturating concentrations (6 mM) of alkylacylglycerols were added in the incubation system. The neuronal/glial ratio was 2.6-2.8 in the absence of lipid acceptor or with low concentrations of alkylacylglycerol. Under most favorable conditions, 6.4 and 3.3 nmoles 1-alkyl-2-acyl-sn-glycerophosphorylethanolamine/mg protein/30 min was obtained for neurons and glia, respectively. Various kinetic properties of the 1-alkyl-2-acyl-sn-glycerophosphorylethanolamine synthesizing phosphotransferase activity were found to be similar both in neurons and glia.