Investigations of iodine species distribution of various aqueous solutions of iodine disinfectants and water from equilibrated suspensions of triiodide and pentaiodide resins were done at the University of Colorado for the Center for Space Environmental Health during 1992 and 1993. Direct measurements of three individual iodine species: I-, I2 and I3-, were made. In addition three measures of total titratable iodine species were used.It has been found that I2 and I3- solutions produce a significant fraction of the non-disinfecting species iodide (I-), ranging from 50 to 80% of added iodine, respectively, at pH values of approximately 5. Correspondingly, I2 solutions produce more than twice the concentration of disinfecting iodine species per mass iodine dose than I3- solutions. Both I- and I2 species were found in aqueous extracts of pentaiodide resin, although no soluble species were detected with triiodide resin.