X. = the number of radioactive atoms in compartment i relative to the number in all compartments on the day of return (some persons returned with body burdens), U = twenty-four hour or one liter urine activity concentration at any time post , ‘ ~-1 i) . subject urine excretion rate, &%d ut . -1 fraction of element transferred from GI tract to blood, um rh mh a return, Bq 2 6, fraction of element reaching extracellular fluid that is excreted through the urine pathway, k = instantaneous fraction of atoms removed from the atom ingestion rate per unit time, at, due to factors other than radioactive decay, q = body burden at any time post return, Bq, q = body burden on the day of return, Bq. Using adult average data, two consecutive urine or body-burden measure- ments were used to estimate the unknown value of k, a rate constant describing removal of radioactivity in diet items. This yielded n-1l estimates of k where nm was the number of measured adult average data points for body burden or urine activity concentration during the residence interval. An average value of k was assigned for the entire residence interval during which activity was measured. After the average k was obtained, an estimate of the atom ingestion rate on day of return was calculated based on a value for adult average body burden or urine activity concentration and the time since day of return. This generated n values of the atom ingestion rate on day of return where n was again the number of adult average data points for body burden or urine activity concentration.