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 an 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 that 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 that 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. Although 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.