Vascular leakage causing macular oedema is an important cause of visual loss in retinal vascular disorders such as diabetic retinopathy and retinal vein occlusion. By digitising selected frames from fundus fluorescein angiographic sequences we have developed a technique which uses the observed rate of change of fluorescence to detect and quantify areas of leakage. Reproducibility studies yielded a coefficient of variation of less than 6% for large areas of leakage, and 27% for very small areas of leakage. We believe this technique is sufficiently sensitive and robust for clinical use, and should find a significant role in the management of retinal vascular disorders.