We measured the endothelial permeability to fluorescein of 30 clear corneal transplants from one to six years after keratoplasty. The mean permeability of 1.51 +/- 0.82 X 10(-4) cm/min was significantly lower than that of normal corneas (P less than .00001). We detected a statistically significant negative correlation between permeability and mean endothelial cell size (P less than .03), indicating that corneas with larger endothelial cells tended to be less permeable to fluorescein. We calculated a relative endothelial pump rate for each cornea; the pump rate was also decreased and negatively correlated with mean endothelial cell size (P less than .0004).