Based on our present understanding of the mechanisms of freezing injury and cryoprotection, we can now design the protocols for introduction and removal of cryoprotectants and for freezing and thawing on a logical and methodical basis. To do this, it is necessary to obtain information regarding the limits of osmotic tolerance and the kinetics of cryoprotectant penetration for the cell type in question. Although this is a straightforward procedure for a given cell type, the situation remains complex for intact organs. Since the organ consists of a variety of cell types, and since survival of the organ presumably depends upon the survival of all of its component cell types, information regarding these parameters must be obtained for all of the dominant cell types in the organ and the cryopreservation protocol tailored to accommodate the least tolerant of the components. We therefore propose to examine individual cell types within the kidney, particularly the vascular endothelium and the tubular cells. Past experience with kidney freezing has shown these two locations to be particularly vulnerable to freezing injury. Basic studies already in progress directed at exploring the ability of certain solutes to increase cell tolerance to osmotic stress will be continued as will some studies on the use of hydrostatic pressure to augment the effects of cryoprotectants.