Abstract. A mathematical analysis of results from kinetic studies of 125‐iododeoxyuri‐dine uptake and loss in almost all the lymphoid and non‐lymphoid organs of mice is described. Applied to data gathered from a graft‐versus‐host reaction experiment, this analysis affords quantitative precision on the differential effects of organ alloantigens on the proliferating grafted cells. It is shown that, depending on the organ and the post‐graft period, cell growth can be ascribed to alloantigen‐driven cell renewal or to alloantigen‐driven trapping or sequestration. Possible applications of the present approach in graft rejection monitoring are discussed.