The method of McWeeny for estimating magnetic effects due toπelectrons in condensed, benzenoid hydrocarbons is applied to calculate the 97 distinct ‘ring currents’, and sigma ratios (H′/H′benzene) for the 219 chemically-non-equivalent protons in the 21 planar hexacyclic benzenoid hydrocarbons which have been synthesized. Trends in the ‘ring currents’ and sigma ratios are discussed; the ‘ring currents’ are useful for culculating diamagnetic anisotropies, and the sigma ratios can be converted to calculated chemical shifts by use of a previously established empirical equation. These shifts are expected to be of use in assigning signals in the experimental high-resolution P.M.R. spectra of these molecules.