We have used nuclear fluorescent dyes to develop a technique for the study of vascular structure and function. Nuclear stained blood vessels, viewed with the appropriate filter sets, can be studied in great detail. Only the nuclei of the cells which form the walls are visible and so their positions relative to one another as well as their viability can be quickly assessed. The dyes are not toxic, therefore when the vessel contracts or relaxes, the changes in position of the nuclei can be monitored. In this paper we describe two original applications of fluorescent nuclear dyes in vascular research.