The detailed conformational analysis of a single molecule of the tetraacyl biosynthetic precursor-type lipid A and its characteristic supramolecular assembly in aqueous SDS-micelles are described. Regular molecular arrangements were observed by detailed analysis of the NMR spectra of synthetically pure specimens, including regiospecifically ¹³C-labeled ones. NMR analysis of a biologically inactive precursor-type analogue with four shorter acyl chains demonstrated its conformational flexibility, indicating the importance of hydrophobic interactions for maintaining the conformation of such molecules.