The effectts of variable periods of ischaemia on the isolated lungs of rats and rabbits, stored for up to 6 hours at 4 degrees C, 21 degrees C and 37 degrees C under standardized conditions, were investigated in vitro in terms of oxygen consumption, the rate of 1-14C-leucine incorporation into soluble proteins, and 1-14C-palmitate incorporation into total phospholipids and lipid fractions. The endogenous oxygen uptake of rat lung slices in an air phase, from tissues stored at 4 degrees C and 21 degrees C under ischaemic conditions for 6 hours and at 37 degrees C for 4 hours, was significantly different from the control values. The oxygen uptake of lungs from animals anaesthetized with pentobarbitone prior to exsanguination and stored for only 2 hours at 37 degrees C differed significantly from control values. Judged by the rate of incorporation of radiolabelled leucine into soluble proteins and that of palmitate into total lipids and phospholipids of lungs after storage for increasing periods at 4 degrees C and 37 degrees C, significant differences were already found after 1 1/2 hours. From this observation it would appear that these parameters are very sensitive indicators for assessing irreversible lung damage due to ischaemia.