Ammonium dihydrogen orthophosphate (ADP) single crystals were grown with L-proline and L-arginine amino acids as additives at 4% molar concentrations. X-ray diffractograms, vibrational FT-IR, and Raman and NMR MAS of (31)P and (1)H spectra of pure and treated compounds were recorded at room temperature and interpreted. A shift of the wavenumbers of some internal modes of both PO(4) and NH(4) tetrahedrons species was observed. At the same time, some characteristic vibrational modes of N-H and C-H bonds of the organic molecules appeared in IR spectra. However, NMR results show a little shift of the resonance of the phosphorus and hydrogen nucleus, associated with some shoulders for this latter. These observations indicate that the host-additives interactions were achieved. (C) 2011 Published by Elsevier B.V.