The electronic excitations and frequency-dependent electronic second hyperpolarizability gamma(-omega;omega,omega,-omega) of the five-ring heterocycles furan, thiophene, selenophene, and tellurophene have been reinvestigated using time-dependent density functional theory. Aspects of basis set saturation, the performance of exchange-correlation potentials, and relativistic effects are discussed. Increased hyperpolarizabilities for molecular dimer species suggest that intermolecular interactions may provide a simple explanation for the large deviations between recent ab initio calculations and experimental condensed-phase data.