The standard (p(o) = 0.1 MPa) enthalpies of formation Delta(f)H(m)(o)(cr) at the temperature T = 298.15 K were determined using static-bomb calorimetry for crystalline 5-methoxybenzofurazan (5MeOBFN), 5-methoxybenzofurazan-1-oxide (4MeOBFNO), 5-methylbenzofurazan-1-oxide (5MeBFNO), and 4-nitrobenzofurazan-1-oxide (4NO(2)BFNO); using rotating-bomb calorimetry for 5-chlorobenzofurazan-1-oxide (5CIBFNO). The standard enthalpies of sublimation Delta(cr)(g)H(m)(o) at T = 298.15 K were measured by microcalorimetry and, from the enthalpies of formation of the gaseous compounds, the dissociation enthalpies D-m(o) of the (N+-O-) dative covalent bonds were derived.