The composition of two glutaraldehyde solutions with different grades of purity was studied by HPLC, UV, J-H and13C NMR spectroscopy. The reactions between various amino acids and the two glutaraldehyde solutions were investigated by UV spectrophotometry. The impurities in the most impure glutaraldehyde solution could be characterized with UV giving a 235 nm absorption, with HPLC as two peaks with retention times 3.36 and 5.78 min and with13C NMR as small signals in the 102.7-94.9 ppm area. It is proposed that the two glutaraldehyde solutions give different reaction products with amino acids.