Information from classical infrared spectroscopy studies has been of significance for characterizing seaweed galactans . The development of Fourier transform infrared spectroscopy and of Fourier transform laser Raman spectroscopy has produced great advances in the application of vibrational spectroscopy to the structural study of polysaccharides . Computational facilities in the spectrometers allow the arithmetic manipulations of the spectra .The second-derivative mode in the FT IR spectrocopy provided more information by increasing the number and resolution of the bands in the spectra as compared to the parent ones . A review of literature data on vibrational spectroscopy of sulfated polysaccharides and new results are presented. Agar-type polymers showed two diagnostic bands in the second-derivative mode in the region 800-700 cm -1 . Carrageenans exhibited a number of bands in the region 1600-1000 cm -1 . Fourier transform laser Raman spectroscopy in the solid state gave well-defined characteristic spectra of agar and carrageenans . Both techniques can be applied to small samples in the solid state and allow differentiation in a few minutes between agar and carrageenan-type seaweed galactans . The second-derivative mode of the FT-IR spectra can be applied to distinguish agar-producing from carrageenan-producing seaweeds . The spectra on KBr pellets of dried, ground agarophyte and carrageenophyte seaweed samples showed the same bands as the corresponding polysaccharides .