It is well documented that vascular endothelial cells constitute an unusually quiescent epithelial cell population. These slowly dividing cells are known to undergo more rapid division in association with wound healing as well as a variety of pathologic conditions such as tumor vascularization and diabetic retinopathy. Although the precise mechanisms responsible for vascular quiescence have not been elucidated, some insights into the regulators of vascular growth control are beginning to be gained. Nearly all of the investigations have utilized cultured vascular cells. Regulation of vascular endothelial growth by polypeptide growth regulators, extracellular matrix molecules, cell-cell interactions, and mechanical forces has been demonstrated in these tissue culture systems.