[en] The biological effect by once chest fluoroscopy had been observated in 42 health persons, in which mean exposure dose of surface of body irradiated in chest fluoroscopy was 1.58 R and red bone-marrow doses was 0.75 rad in male, 0.61 rad in female. The results show loss of activity of red cell C₃b receptor, raise of lymphocyte glycogen and increase of the frequencies of lymphocyte chromosome aberration after exposure of x-ray fluoroscopy. The value of observation was statistically significant between before and after chest fluoroscopy