The absorption spectra of the iodine complexes of a large number of starch-type polysaccharides have been measured. Amylopectins and glycogens show maximum absorption at ca. 540 and ca. 460 mp respectively. This dissimilarity may be correlated with differences in type of iodine-binding arising from variations in the average length of the interior chains of the two polysaccharide-types. Mammalian glycogens are more iodophilic than invertebrate glycogens; this fact cannot at present be related to known structural features.Addition of ammonium sulphate and other salts to a polysaccharideiodine solution causes a marked increase in the iodine-staining power of glycogen, but only a small increase with amylopectin. Under these conditions, the position of maximum absorption is approximately related to the degree of branching in the polysaccharide.