The Raman spectra of kappa and iota carrageenan, a desulphated furcellaran and a series of oligomers have been compared in the region 700-1500 cm-1. Spectral differences depending on the amount and the location of the sulphate group on the ring, the chain length, the nature of the counterion and the conformation are discussed. Indications that the ionic interactions in the Na+ salts of the oligomers are different from those in K+ and Rb+ salts are given. On the macromolecular level it is found that the vibrational movements of the skeleton are related to the chain flexibility and the conformation. In gels of K+ and Rb+ kappa carrageenan spectral evidence is given for the existence of structural order.