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Background: Synovium is the only tissue that can produce hyaline cartilage in benign conditions, such as synovial chondromatosis and osteoarthritis, suggesting potential advantages in chondrogenesis using mesenchymal stromal cells. We performed surface characterization of cells isolated from the synovium of patients with osteoarthritis after different passages and induced chondrogenic differentiation., Methods: Using cells obtained from synovium, colony-forming unit fibroblast assay and characterization of cell-surface markers by flow cytometry using 22 different Ab at different passages were performed. Cells were cultured under chondrogenic conditions and evaluated grossly, histologically, immunohistochemically and by [(35)S]sulfate incorporation and reverse transcription-PCR., Results: The positive cell-surface markers of immediately isolated cells were CD10, CD13, CD14, CD34, CD44, CD45, CD49a, CD62e, CD73 and HLA-DR. After the first passage (P), CD14, CD34, CD45, CD62e and HLA-DR disappeared, whereas CD105 and CD166 appeared and CD10, CD13, CD44, CD49a and CD73 showed increased expression levels. The surface marker expression level did not vary much after P1 through to P8. The chondrogenic differentiation potential of cells from the synovium was confirmed using various evaluation methods., Discussion: We have demonstrated that cells from synovium contain a mesenchymal stromal cell population capable of chondrogenic differentiation, which seems to increase with passage under our culture conditions. The cell-surface markers were found to change remarkably after the first passage and then remained stable. The results of this study may be helpful for sorting mesenchymal stromal cells from heterogeneous synovial cells for future studies.