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An historical analysis of granulomas and a new morphological concept and classification of granulomatous inflammation, the polar-granulomas, are presented. The historical analysis of the concept of granulomas reveals that the still proclaimed confusion concerning the process was due more to Virchow's comparison of granulomas to ordinary granulation tissue than to tumors and to objections of pathologists to Metchnikoff's theory of phagocytosis. And it is strange to verify that differences between granulomas and granulation tissue, although already established in the end of the 19th Century, were overlooked by the majority of pathologists. In this Century , the knowledge of granulomatous inflammation was greatly improved by Aschoff 's concept of reticulum endothelial system, Mitsuda test for types of leprosy, Jadassohn- Lewandowsky law, South American classification of leprosy into polar forms, and Forbus contribution to histogenesis and morphological classification of granulomas. The best model for the study of granulomatous inflammation is leprosy, because this disease is characterized by two different clinical polar forms, each one having particular types of phagocytosis (complete or incomplete) and of granulomas (tuberculoid or non tuberculoid). Based on the phenomenon of phagocytosis, polar forms of leprosy, Jadassohn- Lewandowsky law, metamorphosis of macrophages and nature of the etiologic agent, granulomas can be defined as a reactional hyperplasia of macrophages towards inanimate agents and towards animate agents of low virulence. Also based in the same data, a morphological classification of granulomas into polar types, tuberculoid and non tuberculoid, is proposed. The polar tuberculoid type follows the Jadassohn- Lewandowsky law, its etiologic agent is absent or scarce (complete phagocytosis) - and comprise two sub-types: tubercle-like and sarcoid-like. The polar non tuberculoid type does not follow the Jadassohn- Lewandowsky law, its etiologic agent is always present or copious (incomplete phagocytosis) and comprises two sub-types: giant cell and persistent macrophage. In the latter case, macrophages behave as a culture medium cell or as a storage cell. When both polar tuberculoid and non tuberculoid structures are found together in the same disease, granuloma can be called interpolar . If both types occur simultaneously in the same disease, granuloma would be bipolar. It seems that the proposed definition of granulomas combines morphology with functional activity of macrophages, easily observed in routine histopathological examination by optical microscopy. This morphological classification into polar granulomas (ABSTRACT TRUNCATED AT 250 WORDS)