The study by Gimbrone, Cotran, and Folkman describes the culture and growth characteristics of human endothelial cells derived from umbilical veins. The cells were isolated using collagenase treatment and cultured in Medium 199 supplemented with fetal calf serum. Initially, small clusters of cells spread on plastic or glass and coalesced to form confluent monolayers of polygonal cells within 7 days. These cells were identified as endothelium by the presence of Weibel-Palade bodies, which are characteristic of endothelial cells. The authors observed that endothelial cell cultures exhibit density-dependent DNA synthesis, with higher labeling indices in peripheral growing regions compared to central regions. In confluent cultures, labeling was uniform. When small areas of confluent cultures were denuded, there was localized increases in [³H]thymidine labeling and eventual reconstitution of the monolayer. Liquid scintillation measurements confirmed a correlation between DNA synthesis and cell density. The study suggests that endothelial cell cultures can be useful for studying pathophysiologic factors in endothelial regeneration.The study by Gimbrone, Cotran, and Folkman describes the culture and growth characteristics of human endothelial cells derived from umbilical veins. The cells were isolated using collagenase treatment and cultured in Medium 199 supplemented with fetal calf serum. Initially, small clusters of cells spread on plastic or glass and coalesced to form confluent monolayers of polygonal cells within 7 days. These cells were identified as endothelium by the presence of Weibel-Palade bodies, which are characteristic of endothelial cells. The authors observed that endothelial cell cultures exhibit density-dependent DNA synthesis, with higher labeling indices in peripheral growing regions compared to central regions. In confluent cultures, labeling was uniform. When small areas of confluent cultures were denuded, there was localized increases in [³H]thymidine labeling and eventual reconstitution of the monolayer. Liquid scintillation measurements confirmed a correlation between DNA synthesis and cell density. The study suggests that endothelial cell cultures can be useful for studying pathophysiologic factors in endothelial regeneration.