In rat liver and kidney preservation, hepatic and renal uptake of3 H-adenosine, 3H-glutathione, and 3H-raffinose from University of Wisconsin solution and diffusion to the interstitial space were measured. At 4°C only 0.38±0.47% and 2±0.92% of the total3 H-adenosine remained in the kidney and in the liver, respectively, but at 37°C the amount remaining was 1±1% and 12±3%(P<0.001). Hepatic and renal uptake of the impermeant3 H-raffinose was unaffected by temperature. During flush out, interstitial accumulation of adenosine was significantly higher in livers than in kidneys and decreased during 24-h cold storage. Glutathione accumulation in the interstitial space was two orders of magnitude lower than3 H-adenosine accumulation and comparable to the impermeant raffinose. In summary, the bioavailability of components of preservation solutions at 4°C is lower than at physiological temperatures, so that the application of cytoprotectants at 37°C to organ donors, rather than simple addition to the cold storage solution, might improve cold storage preservation of livers and kidneys.