The solubilities of crystalline NaI, KI and CsI in supercritical ammonia (SCA) were determined for temperatures around 420 K and different ammonia densities smaller than the critical density using the spectral charge-transfer-to-solvent (ctts) band of iodides. The optical absorptivity of the ctts band was also determined with the potassium salt and shown to be density independent. The results show that the solubility of the alkali metal iodides exhibit a very simple dependence on fluid density; this implies that over the density range we have explored, the first solvation shell of the ion pairs is mostly complete even at the lowest studied density. (c) 2005 Elsevier B.V. All rights reserved.