N-Acylethanolamines elicited much interest in recent years owing to their occurrence in biological membranes under conditions of stress as well as under normal conditions. The molecular conformation, packing properties and intermolecular interactions of N-myristoylethanolamine (NMEA) have been determined by single crystal X-ray diffraction analysis. The lipid crystallized in the space group P21/a with unit cell dimensions: a=9.001, b=4.8761, c=39. 080. There are four symmetry-related molecules in the monoclinic unit cell. The molecules are organized in a tail-to-tail fashion, similar to the arrangement in a bilayer membrane. The hydrophobic acyl chain of the NMEA molecule is tilted with respect to the bilayer normal by an angle of 37 degrees. Each hydroxy group forms two hydrogen bonds, one as a donor and the other as an acceptor, with the hydroxy groups of molecules in the opposing leaflet. These O-H...O hydrogen bonds form an extended, zig-zag type network along the b-axis. In addition, the N-H and C=O groups of adjacent molecules are involved in N-H...O hydrogen bonds, which also connect adjacent molecules along the b-axis.