A cell-line was established from bovine placental cotyledon. When cultured in M199 with 10% fetal bovine serum, this cell-line had a doubling time of about 18 h. With immunohistochemistry, it was demonstrated that this cell-line expressed vimentin and angiotensin-converting enzyme (ACE). While both molecules are expressed in endothelial cells, ACE is usually considered to be a specific marker for endothelial cells. Furthermore, cells were shown to take up Dil-Ac-LDL (acetylated low-density lipoprotein labeled with 1,1′-dioctadecyl-3,3,3′-tetramethylindo-carbocyanine perchlorate). This characteristic feature has been used to identify endothelial cells. Finally, when cultured on matrigel, this cell-line formed tube-like structures similar to those formed by endothelial cells. Tube-formation on matrigel is a physiological property specific to endothelial cells. In conclusion, these three lines of evidence strongly suggest that this cell-line is endothelial cell in nature. Further studies using an endothelial cell-line from bovine placenta may help to elucidate the cause of bovine placental retention, a major cause for economic loss in bovine industry. Furthermore, an endothelial cell-line could be an important tool in research areas such as tissue remodeling, angiogenesis, and cancer.