The potential physiological role of plasmalemmal large conductance calcium-activated potassium channels (BK_Ca) in vascular endothelial cells is controversial. Studies of freshly isolated and cultured vascular endothelial cells provide disparate results; both supporting and refuting a role for BK_Ca in endothelial function. Most studies using freshly isolated, intact, healthy arteries provide little support for a physiological role for BK_Ca in the endothelium, although recent work suggests that this may not be the case in diseased vessels. In isolated and cultured vascular endothelial cells, the autocrine action of growth factors, hormones and vasoactive substances results in phenotypic drift. Such induced heterogeneity is likely a primary factor accounting for the apparent differences, and often enhanced BK_Ca expression and function, in isolated and cultured vascular endothelial cells. In a similar manner, heterogeneity in endothelial BK_Ca expression and function in intact arteries may be representative of normal and disease states; BK_Ca being absent in normal intact artery endothelium and upregulated in disease where dysfunction induces signals which alter channel expression and function. Indeed, in some intact vessels, there is evidence for the presence of BK_Ca, such as mRNA and / or specific BK subunits; an observation which is consistent with the potential for rapid upregulation, as may occur in disease. This perspective proposes that the disparity in the results obtained for BK_Ca expression and function from freshly isolated and cultured vascular endothelial cells is largely due to variability in experimental conditions and, furthermore, that the expression of BK_Ca in intact artery endothelium is primarily associated with disease. Whilst answers to physiologically relevant questions may only be available in atypical physiological conditions, such as those of isolation and culture, the limitations of these methods require open and objective recognition.