A series of experiments were run on the retention of inhaled radon. Th
e radon absorbed by the body is present in a multiphase system, showin
g five distinct elimination coefficients. After high-level radon expos
ure for a normal working day, an appreciable breath radon output is fo
und 72 h after removal from exposure. This is a practical consideratio
n in breath radon sampling, and it must be realized that the breath me
asurement may indicate a higher body radium content than that actually
present. Another valuable result is that the radon retention figures
allow us to reconcile the results of breath radon analyses and total b
ody radium analyses on unexposed persons. The results of our breath me
asurements averaged 6x10(-9) g on ten unexposed individuals. It is app
arent that the breath radon measurement is not capable of measuring no
rmal body radium, due both to the small quantity present, and to the i
nterference of radon absorbed by the body from the normal environment.