The gaseous monohalide, dihalide, and trihalide species in the Dy-Br and Dy-I systems were generated by the reactions of Br-2(g) and I-2(g) with Dy(s) in a heated effusion cell reactor, and equilibria among these species were studied in the range of 1300-1500 K by means of mass spectrometric monitoring. Reaction enthalpies were evaluated from third-law analysis of the equilibrium data and were used to derive the individual bond dissociation energies (BDE) in the species and related thermochemical properties. The analysis yielded the selected BDE values at 298 K: D(Dy-Br) = 81.1 +/- 2.5, D(BrDy-Br) = 96.1 +/- 3.2, and D(Br2Dy-Br) = 106.0 +/- 3.8 kcal mol(-1); and D(Dy-I) = 64.3 +/- 2, D(I2Dy-I) = 80.1 +/- 2.8, and D(I2Dy-I) = 82.8 +/- 13.5 kcal mol-1. Bond energy sums in the two trihalides are in reasonable agreement with atomization enthalpies derived from sublimation data. D-0(o) values of DyBr and DyI are compared with recent estimates based on ligand field theory.