The standard (p(o) = 0.1 MPa) molar enthalpies of combustion in oxygen, at T = 298.15 K, for crystalline 2-iodosobenzoic acid, (OI)C6H4COOH, and 4-nitrosophenol, (ON)C6H4OH, were measured by rotating-bomb calorimetry and static-bomb calorimetry, respectively. These values were used to derive the standard molar enthalpies of formation of the crystalline compounds. [GRAPHICS] An indirect method was used for assessing the dissociation enthalpy of the (I-O) bond in the iodoso derivative, D-m(o)(I-O)/(kJ . mol(-1)) = (264.5 +/- 8.1), which is the first value reported for an iodine-oxygen bond in an organic molecule.