PbO and PbO- were studied utilizing CCSD(T), CASSCF/CASPT2, and the Fock Space FSCCSD methods. Relativistic effects were treated by the spin-free, two-component infinite-order Douglas-Kroll-Hess, Dirac-Coulomb and the restricted active space state interaction RASSI-SO methods. Our adiabatic electron affinity (EA), 0.696 eV, agrees favorably with experiment (0.714 eV). Theoretical dissociation energies D-e of PbO and PbO- (3.91 and 3.20 eV) differ from experiment by 0.04 and 0.07 eV, respectively. The electron correlation, relativistic scalar and spin-orbit effects are crucial for obtaining good agreement of theoretical and experimental data for EA and D-e. Equilibrium bond distance and vibrational frequency are less sensitive to SO effects. (c) 2005 Elseiver B.V. All rights reserved.