Local density functional (LDF) calculations with polarized double-xi basis sets have been used to calculate the two lowest one-electron ionization potentials (IPs) of a variety of free base porphyrins with multiple alkyl, aryl, fluoro, chloro, bromo, trifluoromethyl, cyano, and nitro substituents. For unsubstituted porphyrin (PH2), beta-octaalkylporphyrins, and meso-tetraphenylporphyrin (TPPH2), LDF-Delta SCF calculations reproduce the lowest ultraviolet photoelectron spectral (UPS) IPs to within similar to 0.2 eV. The two lowest one-electron IPs of TPPH2 are predicted to be lower than those of PH2 by similar to 0.5 eV, in agreement with UPS experiments. Ab initio Hartree-Fock (HF) theory seriously underestimates this electronic effect of meso-tetraphenyl substitution.