The standard (p(o) = 0.1 MPa) molar enthalpies of formation of five crystalline halogen-substituted 8-hydroxyquinolines, at the temperature T = 298.15 K, were derived from measurements of the standard molar enthalpies of combustion in oxygen by rotating-bomb calorimetry. Delta(f)H(m)(o)(cr)/(kJ . mol(-1)) 5-chloro-8-hydroxyquinoline C9H5NCl(OH) -124.2 +/- 1.9 5,7-dichloro-8-hydroxyquinoline C9H4NCl2(OH) -158.1 +/- 1.8 5,7-dibromo-8-hydroxyquinoline C9H4NBr2(OH) -40.5 +/- 2.8 7-bromo-5-chloro-8-hydroxyquinoline C9H4NBrCl(OH) -127.7 +/- 2.1 5,7-diiodo-8-hydroxyquinoline C9H4NI2(OH) +93.5 +/- 1.7 Using literature values of their standard molar enthalpies of sublimation, the standard molar enthalpies of formation, at T = 298.15 K, of the gaseous compounds were derived. These values are compared with those estimated by means of structural contributions.