The authors made a detailed clinical analysis of 119 stabilized total paraplegics in order to define, as precisely as possible, the limits of the medullary segment which, for each patient, had lost all its functional value. The relationships between the affected segments and the sexual capabilities of these patients show that the segment must: --exclude the sacral spinal cord if reflex erections are to occur; --underly Th. IX at least, or better still Th. XI, for psychogenic turgescence to appear; the efferent pathways seem therefore, to emerge from the cord quite close to the level which receives testicular afferent pathways; --underly or overly Th. XII, L I, and L II for at least the greater part, for emission of sperm to occur; a true abrupt ejaculation probably requires the complementary integrity of the sacral spinal cord.