Glycogen-iodine (GI) complex formation has been studied at different concentrations of iodine and glycogen. For each glycogen concentration (0.25, 0.125, 0.0625, 0.0313 g/L), the iodine concentration was varied from 0.0317 to 1.59 g/L and the absorbance readings were taken at 453 and 560 nm (GI wavelengths of maximum absorbance). The 453 nm absorbance curves for the GI solution (GI complex and unreacted iodine), and that of the pure iodine solution (without glycogen) level off at a high iodine concentration, and give a peak in the subtracted curve. The 560 nm curves consistently increase in absorbance, and no peak is noticed in the subtracted curve. The spectra of concentrated iodine solutions in water and alcohol suggest the formation of neutral iodine clusters. We suggest that these iodine clusters do not react with glycogen, and that the GI complex formation takes place by the addition of I-2 molecules.