[en] This paper studies the DNA-synthetic activity of hyman embryonic cells (EC) cultured in the presence of supernatants from intact and irradiated cell fractions of blood or plasma. Human EC obtained from abortion material were incubated; after incubation, tritium-thymidine was added to the growth medium for 30 min. It is shown that stimulation of DNA synthesis in EC growing in the presence of supernatants from irradiated whole blood is not connected with photoactivation of growth factors in the blood plasma, but takes place as a result of their release from the cells. Donated blood, irradiated with UV light of the same wavelength and within the same dose range as are used under clinical conditions (up to 1200 J/m²), possesses growth-stimulating properties