In the mid-1990s, my research group began to devise a method to establish endothelial cell cultures from human peripheral blood, with an ultimate goal of examining interindividual heterogeneity of endothelial biology. The initial work, published in the JCI in 2000, described the method enabling successful attainment of blood outgrowth endothelial cells (BOEC). Truly endothelial, BOEC are progeny of a transplantable cell that originates in bone marrow, a putative endothelial progenitor. Our subsequent experimental work focused upon practical applications of BOEC: their use for gene therapy, tissue engineering, assessment of mutant gene effect, and discovery of heterogeneity in endothelial biology.