The conformation of hexadecylphosphocholine (HPC) and its interaction with model membranes prepared from dipalmitoylphosphatidylcholine (DPPC) have been investigated by molecular dynamics (MD) and NMR methods. The results of MD studies indicate that in the global minimum energy structure, the phosphocholine head group of the drug is bent at τ 1 8 and τ 1 9 , while the hexadecyl chain is nearly extended. In the two-dimensional nuclear Overhauser effect (NOE) experiments, intramolecular NOEs have been observed between the N-methyl moieties of the head group and the methylene protons of the alkyl chain. Such a folding of the molecule is seen in several of the local minimum energy structures computed by MD simulations. The interaction of HPC with DPPC as studied by 3 1 P NMR shows a strong interaction between head groups of the two molecules.