This brief review discusses the ways, if and when available, to examine end
othelium-dependent changes in diameter in human blood vessels. It stresses
the problems in ensuring proper matching between arteries (and veins) from
different human sources. It briefly considers the evidence in vitro support
ing the role of endothelium-derived nitric oxide, hyperpolarizing factor(s)
and contracting factors (including metabolites of arachidonic acid and end
othelin), It emphasizes the difficulty in extrapolating observations obtain
ed in isolated arteries (and veins) to the intact human circulation. The ov
erall conclusion is that the interpretations derived from animal work apply
to the human vasculature. J Hypertens 1999, 17:1047-1058 (C) Lippincott Wi
lliams & Wilkins.