Endothelial cells are intimately involved in a wide range of biological processes including reproduction, development and wound healing (Folkman, 1992), as well as pathological processes such as inflammatory disorders of the skin and joints (Abbot et al., 1992), diabetic retinopathy and tumour invasion (Folkman, 1992). This has led to major efforts over the past twenty years to isolate and culture endothelial cells from both animal and human tissues, in order to investigate their role further. The most common isolation has been from the human umbilical vein, largely because of the ease with which the umbilici can be obtained. Isolation involves cannulation of the vein and introduction of a proteolytic enzyme, followed by a five to fifteen minute incubation before flushing to yield an isolate of endothelial cells (Jaffe et al., 1973). Alternatively, it is possible to obtain endothelial cells from large vessels, including arteries, by gentle scraping of the intimal surface with, for example, a cotton-wool tip.