Ab initio calculations of dipole moments and static dipole polarizabilities are reported for nine heteroaromatic five-membered rings-thiophene, thiazole, isothiazole, the four thiadiazoles, and the two thiatriazoles-all at their MP2/6-31G** geometries. Extensive basis sets have been used, and the approximate applicability of the variational principle to the Hartree-Fock polarizability has been discussed. Electron correlation effects have been investigated up to the MP4(SDQ) level for a representative subset of the series of the molecules considered. Our best polarizability determinations are expected to be accurate within a few percent.