The standard (p degrees = 0.1 MPa) molar enthalpies of formation Delta(f)H(m) degrees for liquid 2- and 3-chloropyridine, and crystalline 2,3-, 2,5-, 2,6-, and 3,5-dichloropyridine were derived from the standard molar enthalpies of combustion Delta(c)H(m) degrees at T = 298.15 K in oxygen using rotating-bomb combustion calorimetry. The reaction products were : CO2(g), N-2(g), and HCl . 600H(2)O(1). The standard molar enthalpies of vaporization, or sublimation Delta (Hcr,lHm)-H-g degrees at T = 298.15 K were measured by Calvet microcalorimetry. The results are as follows:[GRAPHICS]The derived standard molar enthalpies of formation in the gaseous state are shown to fit a group additivity scheme.