The conditions under which the Hückel molecular orbital (HMO) treatment of inductive substituent effects can be expected to be reliable are discussed from the viewpoint of the Pariser-Parr-Pople (PPP) model. The HMO theory fails to predict correctly the direction of the shift of the first intense band in the ultraviolet spectrum of fluoranthene (“1→−1” transition) on 3-aza “substitution”. Calculations on the five azafluoranthenes using the simple version of the PPP method suggest that this is due to strong mixing of hydrocarbon states by the effect of the “substituent” and predict significant changes in energies, intensities, and polarizations of fluoranthene electronic transitions on aza “substitution”. Transition moment directions derived from dichroic absorption of 3-azafluoranthene in stretched polyethylene sheets are in agreement with PPP predictions. Arguments are given against a previous assignment of the first transition in 1-az