The standard molar dissolution enthalpies of metallic orthoperiodates hydrates salts of the type, M2HIO6.nH(2)O (M = Cu2+, Zn2+, Cd2+; n = 2, 1.25, 1.25), in aqueous 3 mol dm(-3) HNO3 have been measured by using an isoperibolic calorimeter at 298.2 K. The thermodynamic parameters of these compounds, e.g. Delta(diss)G(m)degrees and Delta(diss)S(m)degrees, have been calculated or estimated. The related values published in the literature and that were obtained from solubility determinations using a spectrophotometer in the 298.5-328 K temperature range have been also revised by using a linear regression analysis.