This work deals with the characterisation of the dielectric secondary relaxations of poly(allyl alcohol) (PAA) and poly(vinyl alcohol) (PVA) and its comparison with the cellulose and dextran dielectric behaviour. Cellulose and dextran are two polysaccharides made of glucosyl repeat units. Cellulose has two hydroxyl groups (OH) and one hydroxymethyl group (CH2OH) per glucose ring, while dextran has three OH groups and no CH2OH group. PAA and PVA are the two simplest vinyl polymers containing CH2OH and OH lateral groups, respectively. They exhibit only one broad dielectric secondary relaxation with characteristics in between those of the gamma and beta mechanical relaxations in drie d PAA. Each of these apparently unique relaxations is successfully explained and modelled by the overlaps of two relaxation processes, gamma ' and beta '. The gamma ' relaxation, related to the rotation of side groups (CH2OH for PAA and OH for PVA), has characteristics close to those of the gamma mechanical relaxation for dried PAA. The beta ' relaxation corresponds to more or less cooperative motions of main-chain segments. Furthermore, the influence of moisture on the secondary dielectric relaxations of PAA and PVA is discussed on the basis of a competition between gamma ' and beta ', where the intensity of beta ' (gamma ') increases (decreases) with increasing water content. (C) 2001 Published by Elsevier Science Ltd.