The microvasculature consists of endothelial cells (EC) with albuminally located pericytes. A number of clinical and experimental observations suggest that pericytes contribute to the regulation of microvascular growth and function. EC and pericytes appear to have a variety of means whereby they may influence one another, including soluble growth factors, gap junctions and adhesion molecules, to name a few. Co-culture systems have provided a good deal of evidence to support the concept that these two cells interact and that these communications are central to vessel assembly, growth control and normal function.