The molecular structures, vibrational frequencies, and internal rotational potentials of 209 polychlorinated biphenyls were computed at the B3LYP/6-31G(d,p) density functional theory level. Standard entropies, S-o(T), heat capacities, C-p(o)(T), and enthalpies, H-o(T) -H-o(0) (100 K less than or equal to T less than or equal to 1500 K), were calculated using the rigid-rotor harmonic-oscillator approximation with correction for internal rotation. Enthalpies of formation, Delta(f)H(298)(o), were calculated at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d,p) level using isodesmic reactions and the recommended Delta(f)H(298)(o), values for biphenyl, benzene, and polychlorinated benzenes. The uncertainties of the calculated values are estimated to be 5-10 J K-1 mol(-1) for S-298(o), and C-p(o298) and 5-35 U mol(-1) for Delta(f)H(298)(o). The calculated thermodynamic properties are compared with values determined earlier by the semiempirical and group additivity methods.