The dissociation energies of BiO, BiS, BiSe and BiTe were determined from equilibrium studies based on the exchange reactions Pb(g)+ BiX(g)= Bi(g)+ PbX(g), where X = O, S, Se or Te and from the known dissociation energies of PbO, PbS, PbSe and PbTe. The values obtained are D°0(BiO)= 338.9 ± 5.9, D°0(BiS)= 311.8 ± 4.6, D°0(BiSe)= 276.5 ± 5.9 and D°0(BiTe)= 228.5 ± 11.3 kJ mol–1. These are based on the dissociation energies of the PbX molecules which are discussed : D°0(PbO)= 374.0 ± 4.2, D°0(PbS)= 342.3 ± 1.7, D°0(PbSe)= 299.1 ± 4.2, and D°0(PbTe)= 246.1 ± 10.5 kJ mol–1. The latter two also involve a discussion of D°0(Se2)= 329.0 ± 0.3 and D°0(Te2)= 260.7 ± 0.8 kJ mol–1.