A method is described wherein monophosphoinositide is quantitatively extracted from as little as 1 mg of brain, deacylated to glycerophosphoryl inositol, trimethylsilylated and gas chromatographed. Amounts of glycerophosphoryl inositol as small as 5 ng (15 pmoles) have been chromatographed. The flame ionization detector response is linear from this level to 10 μg. This method gives values for monophosphoinositide in excellent agreement with those obtained with much larger tissue samples using the previously available techniques. Other advantages of the gas chromatographic method are its high degree of specificity, due to the increased resolution of the separation technique, and the considerable increase in the speed with which multiple determinations can be carried out.