[en] In experiments on mice and bone marrow CFUs a study was made of the radioprotective efficiency of serotonin and adrenaline depending on their concentration. It was shown that in order to protect the body a minimum amount of monoamines is requred; the amount to protect CFUs in vivo is about 5 times greater, and to protect CFUs in vitro, the dose is maximum. The animals are protected by such monoamine concentrations which cannot lessen the affection of CFUs in vivo