Urinary Radioiodine Excretion at 15 Days J day"! K _ day? x 10° L day" x 10° aly + of 125,day TE 3.7 4.85 7.2 0.050 3.7 4,85 13.8 0,066 3.7 17.15 7.2 0.16 3.7 17.15 13.8 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 jodine in man which will be described more fully in a UCRL report entitled, ''The Dynamics of Lodine in Man."