The author presents his priority of the polar concept in leprosy, and briefly reviews what he calls the history of an idea. The polar concept was first presented in February-May 1938, and was to receive full recognition from the Havana's Committee on Nomeclature and published in the Annals of the 5th International Congress of Leprosy (April 1948). In recent years many points brought by immunopathology focused the humoral immunity at the level of the immuno-negative L pole, in clear-cut opposition to the cell-mediated immunity present in the immuno-positif T pole. Polar concept thus receiving a remarkable physio-pathological support to the views once expressed by the author.