The correlation between the relative intensity of water Raman band and crystal quality was studied for thaumatin and tetragonal lysozyme crystals grown under different conditions. The intensity variation of the band, revealed for the set of crystals was interpreted as being due to the different extents of ordering of internal water molecules. It was suggested that ordering is mainly relative to the alignment of the angle between the O-H bonds in water, since this angle serves as a normal coordinate for the symmetric bending vibration of H-O-H unit and the spectral width of the corresponding Raman band (2v2) at 3212cm-1 appeared to be the main indicator of ordering. The assumption that the ordering of internal water molecules is relative to the overall protein crystal perfectness was verified by comparison of crystal scores obtained via the Raman and diffraction methods. The assessment of the crystal perfectness via these two methods seems to show some correlation. If this correlation confirmed, the noninvasive Raman spectroscopy may be used to monitor crystal quality during its growth. © 2000 Elsevier Science B.V. All rights reserved.