Isomerization of isopropy]idene glycerol ketals and benzylidene glycerol acetals was studied, and isomerization equilibria were established. Reaction of benzaldehyde with glycerol gave four benzylidene glycerol isomers, which were separated by column chromatography and characterized by NMR spectroscopy and other methods.Isomerization of 1-and 2-monoglycerides and of 1,2-and 1,3-diglyeerides, and their separation by column chromatography, are described. Mechanisms of isomerization in mono-and diglycerides and factors which affect them are discussed.Isomerization of 1-and 2-glycerophosphates and of cyclic glycerophosphates by acid and base was also studied. Hydrolysis products of L-3glyeerylphosphorylcholine and 2-glycerylphosphorylcholine were separated by column chromatography and characterized by periodic acid oxidation, optical rotation, and NMR spectroscopy. No isomerization of unhydrolyzed L-3glycerylphosphoryleholine and 2-glyccrylphosphorylcholine was observed. Evidence indicated that acid-catalyzed hydrolyses of phosphoglyeerides are under thermodynamic control whereas most base-catalyzed hydrolyses are under kinetic control.