We report on high resolution photoelectron core level spectroscopy (HRCLS) and scanning tunnelling microscopy (STM) measurements of the decomposition of lysine adsorbed on InP(001) substrates. We find that components from the lysine can be present on the InP surface even after annealing to 600 degrees C and desorption of the native surface oxide. We further observe that while a crystalline surface phase can be observed on the epi-ready surface after annealing, the lysine treated surface still appears rough. We conclude that lysine residues inhibit the formation of a flat crystalline structure on the InP(001) surface. These results are discussed in terms of the lysine promotion of [001] nanowire growth.