The purpose of this project is to study the osmotic behavior of perfused tissues and organs during the introduction and removal of cryoprotective agents (CPAs) from both an analytical and an experimental point of view. Comparison of theoretical predictions of organ behavior during CPA introduction and removal based upon a newly developed non-steady-state mass transfer model with experimental observations of the responses of perfused organs to changes in the composition of their perfusates will-it is hoped-facilitate the development of optimum CPA introduction and removal protocols.