Abstract: The physiological and chemical basis of Di-Region theory proposed by one of the authors is investigated in this paper, and some fundame-tal ideas related to the establishment of Di-Region theory are introduced. Based on Di-Region theoy, we made a tentative research on the discriminating classification of the carcinogenic activities of polycyclic aromatic hydrocarbons (PAH) by the pattern recognition method centred on quantification theory. The results obtained from the discriminating classification of training samples are very close to that of animal experiments. Prediction is made for the carcinogenic activities of some PAH which have not been tested with animals. The consistency of the results of the pattern recognition method and the routine calculation by the di-regional equation provides statistically an evidence for the rationality of the di-regional theory.