There have been consideraole difficulties in developing a satisfactory method for the Cryopreservation of corneas. In this paper we describe the effect of two variables that appear to influence the effectiveness of preservation, the concentration of cryoprotectant and the medium that surrounds the cornea during freezing. Rabbit corneas were exposed to the cryoprotectant dimethyl sulphoxide (Me2SO) in concentrations of 1 or 2 mo1/1 in a high-potassium well-buffered solution, and then cooled to—196°C either in air or surrounded by 5 ml of the Me2SO solution. After storage at-196°C, thawing and removal of the Me2SO, survival was assessed by electron microscopy and measurement of stromai thickness during perfusion on the specular microscope.The least degree of damage was observed when corneas were equilibrated with 1M Me2SO and frozen in air. The evidence suggests that 2M may be an excessive concentration of Me2SO in this system and that damage to the stroma may be reduced by freezing the cornea in air rather than surrounded by the Me2SO solution.