This paper compares harmonic and anharmonic frequencies of pyrrole and furan computed using the B3LYP density functional and medium size basis sets. Anharmonic corrections have been obtained by a perturbative treatment recently introduced by the author in the Gaussian program. Inclusion of anharmonic contributions reduces the absolute average error by nearly an order of magnitude down to about 5 cm(-1). This level of agreement is at least comparable with that of the best scaled quantum mechanical force fields, but is obtained by a completely automatic procedure without any scaling factor. (C) 2003 Elsevier B.V. All rights reserved.