Application of the University of Wisconsin cold storage solution has rapidly expanded to include medium-term to long-term preservation of virtually all intraabdominal organs. Its use in intrathoracic organ transplantation has also been suggested. We therefore examined the efficacy of the University of Wisconsin solution in a primate allotransplantation model for preservation of hearts, and as a simple single-solution system for static preservation of heart-lung blocks, for periods of ischemia ranging from 6 to 24 hours. For comparison, we employed the histidine-tryptophane-ketoglutarate cardioplegic solution of Bretschneider. University of Wisconsin solution provided superior results with regard to clinical outcome and hemodynamic recovery of hearts after ischemic periods of up to 16 hours. This was in contrast to Bretschneider's solution, which allowed storage of hearts for periods of only up to 10 hours. Heart-lung blocks were equally well preserved with either University of Wisconsin or Bretschneider's solution after 6 to 12 hours, although the University of Wisconsin solution group exhibited a more notable increase in pulmonary water content. This was in accordance with histological data, which suggested that, although hemodynamic recovery of hearts stored for periods longer than 10 hours was poor, preservation of pulmonary ultrastructure was far superior using Bretschneider's solution as compared with University of Wisconsin solution after an ischemic period of up to 16 hours.