Wt traction from GI tract to blood, f = fraction excreted by the urine pathway, Kg = instantaneous fraction of atoms removed or added to the atom uptake per unit time, day~!, q = instantaneous body burden, Bq, q° = body burden at the onset of uptake, Bq, D = the number of disintegrations in all compartments occurring during the uptake interval, Bq days. Equations 1 and 2 were used to determine the dietary removal rate constant Ke and then the initial daily activity ingestion rate required to produce the measured or derived body burden. Equation 3 was used to determine the number of disintegrations that occurred in the body during the residence interval of an individual living on Rongelap or Utirik Atoll. DETERMINATION OF Ke If the mean residence time in the diet is much much longer than the resi- dence interval, then constant continuous uptake is achieved. Equations 1 and 2 can be converted to the constant continuous equations by replacing KR, with -i. Single uptake expressions are obtained by setting P® equal to zero, In some cases only radioactive decay may remove the nuclide from dietary items; for these cases Kp would equal zero. In the case of the former Bikini residents, the maturing of coconut trees during regidence on Bikini Atoll caused a continuously increasing dietary uptake of 13766, negative value. tive value for Thus, Ky was found to have a In the case of Rongelap and Utirik, Ke was found to have a posi137, 8; 65 Zn, 60 Co and 90 Sr. This indicated that in addition to radioactive decay, some other removal mechanism decreased the radioactivity in