The standard (p degrees = 0.1 MPa) molar enthalpies of formation Delta(f)H(m) degrees(cr) at the temperature T = 298.15 K were measured by using combustion calorimetry of 2-phenylphenol, 4-phenylphenol, 2,6-diphenylphenol, 2,2＇-dihydroxybiphenyl, and 4,4＇-dihydroxybiphenyl. The standard molar enthalpies of sublimation Delta(cr)(g)H(m) degrees of the compounds were obtained from the temperature variation of the vapour pressure measured in a flow system. Molar enthalpies of fusion Delta(cr)(1)H(m) degrees of the compounds were measured by d.s.c. Values of the weak interactions (about 2kJ.mol(-1) to 4kJ.mol(-1)) of phenyl substituents with the hydroxyl group were derived from the enthalpies of formation in the gas phase.