Both eyes of 16 patients who had undergone unilateral penetrating keratoplasty were examined in this study. The mean corneal oxygen uptake rate in the centre of the graft was 3.88 (SD 0.55) mmHg/s and in the control eye was 4.29 (SD 0.62) mmHg/s. In the temporal host periphery the results for the grafted and control eyes were 4.52 (SD 0.54) mmHg/s and 4.26 (SD 0.52) mmHg/s respectively. The differences in the oxygen uptake rate between the centre of the graft cornea and the contralateral control eye and between the centre and periphery of the graft eye were statistically significant (p less than 0.01). The central corneal touch threshold of the graft eye showed good recovery in four patients, while the remaining 12 had no or minimal recovery. The central and temporal epithelial and corneal thicknesses of the graft and the control eyes were not significantly different. The central endothelial cell density was 1383 cells/mm2 in the graft and 3053 cells/mm2 in the control eye. As corneal oxygen uptake reflects changes in aerobic epithelial metabolism, it is possible that there is a link between loss of neural integrity of graft epithelium and lowered epithelial aerobic metabolism following penetrating keratoplasty.