Urinary Radioiodine Excretion at 15 Days J K L day” day! x 10” day! x 10° 3.7 3.7 3.7 3.7 4.85 4.85 17.15 17.15 7.2 13.8 7.2 13.8 aly, % of 18°day 0.050 0.066 0.16 0.21 On the basis of these calculations the normal range of urinary radioiodine excretion at 15 days was estimated to be 0.05 to 0.2% of the peak thyroid content. The problem outlined above is a practical application of an analytical study on the uptake and excretion of iodine in man which will be described more fully in a UCRL report entitled, "The Dynamics of Iodine in Man."