The vertical electronic spectrum of furan is investigated by second and third-order multireference perturbation theory (NEVPT). The excitation energies of the three lowest-energy valence states, as well as the 3/Rydberg states are reported. The effects of the size of the active space and the valence-Rydberg mixing are discussed. The application of the quasi-degenerate NEVPT approach has proved to be necessary in order to handle the consistent valence-Rydberg interactions occurring for the two (1)A(1)(+) and B-1(2)+ valence states. For the three valence states and the low-lying Rydberg states, the computed excitation energies agree with those computed in the more recent high-level theoretical studies. (c) 2006 Elsevier B.V. All rights reserved.