The distinction between lymphatic and blood vessels is biologically fundamental. Two immortalized cell lines, which have been widely used as models for endothelial cells of blood vascular origin, are the human microvascular endothelial cell line-1 (HMEC-1) and the telomerase-immortalized microvascular endothelial cell line (TIME). However, analysis of protein expression by flow cytometry revealed expression of lymphatic markers on these cell lines. Furthermore, functional in vitro leukocyte transmigration assays demonstrated deficiencies in several steps of the leukocyte extravasation cascade. Hence we performed this microarray analysis of the gene expression in HMEC-1 and TIME. We then compare the expression profiles to those of published blood- and lymphatic endothelial cells.