The use of human omentum as an alternative to veins as a source of cells for seeding onto small-caliber vascular prostheses has awakened controversy as to the identification of the predominant cell type derived from this source. Mesothelial cells from omentum were extracted by collagenase digestion, and cultured until a monolayer was formed. These cells showed positivity for monoclonal antibodies specific for endothelial cells (anti-CD34 QBEND10), antibodies to intermediate filaments (anti-vimentin and anti-desmin) and anti-smooth muscle cell antibodies (anti-actin and anti-total actin). The mesothelial cells behaved like endothelial cells derived from vein when seeded onto polytetrafluoroethylene prostheses, showing high levels of prostacyclin production. This report provides additional evidence of the non-endothelial origin of the cells derived from human omentum.