Electrophilic character is associated with the ability of external agents to interact with centers of electron density in biological macromolecules and to cause the interruption or alternation of normal activity. With the observation of site specificity in mutagenic events, Pearson's hard/soft acid-based (HSAB) theory is presented as a useful concept in correlating chemical observations in the absence of detailed direct knowledge of the process. Methods for the evaluation of carbon electrophiles (e.g., carbocation character) as reactants are reviewed as potential physical parameters that could be applied in developing quantitative structure-activity relationships.