1. Increasing evidence suggests that oestrogens protect women from cardiovascular disease during their reproductive years. Although most studies by others have examined the effect of oestrogen on vascular smooth muscle cells, we have evaluated the effect of oestrogen on the angiogenic behaviour of endothelial cells. 2. Oestrogen enhances endothelial cell attachment, proliferation, migration and organization into capillary-like structures in vitro. In vivo, oestrogen augments experimental angiogenesis. 3. As the same endothelial cell behaviours that are important in angiogenesis in small vessels are also important in the healing response to injury of large vessels, it is likely that the effect of oestrogen on these endothelial cell functions contributes significantly to the cardioprotective effects of oestrogen in women.