When commenting on morphological findings in cerebral vasoconstriction studies, caution is required in two areas, namely the mechanical stresses involved in experimental manipulations, and preparation techniques. Since simultaneous radiological studies are sometimes compared with the results of morphological investigations, clarification of the relationship between morphological findings and the in vivo situation has gained added impartance. In the absence of properly planned control groups, many morphological findings that are, in fact, caused by preparation technique may easily be considered "results." In this study, the ultrastructural effects of two different preparation techniques were evaluated on electron microscopic images of the basilar artery. Ultrastructural changes, such as convoluted lamina elastica intema, cytoplasmic vacuole formation in the endothelium, endothelial denudation, and electron-dense smooth muscle cells with swollen mitochondria and abundant collagenous fibers, were also observed, to a lesser degree, in the control groups.