Descripción: The polysaccharides from cystocarpic Iridaea undulosa, soluble and insoluble in 2M potassium chloride, Cs and Ci, respectively, were treated with alkali and fractionated by precipitation with increasing concentrations of KCl. They were later separated by ion-exchange chromatography, to yield fractions enriched in an α-(1→6)-glucan, agaroids and carrageenans.