A pilot experiment has been performed to determine the feasibility of routine monitoring of α-radionuclides in the bloodstream by immersion of CR-39 in fresh blood with deep freezing at -20°C. Blood samples were collected from 61 volunteers, 50 from the Bristol area and 11 from Sciacca. 30 subjects were smokers and 31 non-smokers. Relative activity values for 210Po and 222Rn and short lived daughter nuclei were obtained for the Bristol samples. These show a level of 210Po twice as high in smokers compared with non-smokers. The results are of intrinsic interest and show that CR-39 may be used in similar applications such as the monitoring of plutonium in the bloodstream in man.