Where realized experimental observations about some animals complements (dogs, rabbits,guines pigs, mens, horses and cows), verificated the action of roentgen radiations and ultraviolet radiations about than. It was found that the studied complements in constant temperature of 10°C, were not destroyed by the roentgen radiations (112.500 r). The same thing did not happen those submited under ultraviolet radiations, these were inactivitates. The time necessary for inativations, changes according with the degre of complements diluitions, when irradiateds. It was found afterwords that the destroyed fraction is- the albumin fraction (second component, C2). The complements so inativated might regenerate their properties by the adition of albumine fractions obtained of complements not irradiated. The regenerating fraction might belong to identical animals and some cases to animals of diferent species. The albumin fraction of guinea pig, complement regenerates the inactivated complements of guinea pig, man, dog and partial rabbits, but it is not regenerated by the albumine fractions of their complements. The albumin fraction of human complement regenerates the inativated complement of man, horse and cow, but it is not regenerated by the albumine fractions, of the last two animals.