Tests are still lacking about the suitability of scanning electron microscopy (SEM) of vascular resin casts to show different functional states of peripheral blood vessels. With the aid of a vitalmicroscopic device, we tried to elaborate a vascular casting method using the model of the albino rat iris vasculature. Functional variations of the vasculature were induced by local application of epinephrine to one eye using the untreated fellow eye as a control. It was found that if our modification of Araldite plastic is injected via a systemic access and without preceding rinsing with fixatives or salt solutions there is a good correlation between the vessel diameters seen in SEM of resin casts and the vessel diameters found in the vitalmicroscopic observations. Thus, this method appears also suitable for studying the effect of vasoactive substances.