The electronic structure of methyl-substituted 1, 2-benzanthracenes, heteroaromatic compounds such as benzcarbazoles, benzacridines and DAB derivatives was calculated by the frontier electron method. A distinct parallelism was found between the frontier electron distribution at the carcinogenophore of these compounds and their carcinogenic activity, Reaction involved in the early stage of carcinogenic action of all chemical carcinogens has been postulated by the present authors to be of nucleophilic nature, and the numerical values of the reactivity indexes in this paper supprt this postulation.