Although lung transplantation represents a real therapeutic opportunity, the problem of preserving the organ for a prolonged period (> 10 h) still remains unsolved. Further studies are necessary to fully understand the behavior of different lung cell types during the ischemic period. As ultrastructural modifications of cells of lung samples stored in different means of preservation represent an index of the integrity and therefore of cellular viability, in the present work we have compared the time-related ultrastructural changes in human pneumocytes type II cells after hypothermic (10 degrees C) storage for 6 and 12 h in University of Wisconsin (UW) solution and in low potassium dextran (LPD) solution. An ultrastructural grading scale was used to quantify the damage and the results confirmed what was observed microscopically. Statistical analysis (t test) of the data showed that after 6 h in LPD solution, pneumocytes type II were less damaged than those stored in UW solution; these differences were statistically significant (p < 0.05). In our opinion, ultrastructural studies should be considered among the methods presently used to assess the effectiveness of different storage fluids.