Adipose-derived stem cells cultured in autologous serum maintain the characteristics of mesenchymal stem cells Human adipose tissue is known to be an attractive and readily available source of mesenchymal stem cells (MSC), which are becoming increasingly popular for application in regenerative medicine. Most of the protocols currently used for in vitro expansion of MSC include fetal bovine serum (FBS) supplementation. When MSC are cultured in such a way for clinical applications this rises concerns about immunogenicity of FBS proteins. A possible solution to this problem is the use of autologous serum (AS) instead of FBS. In this study we investigated whether adipose-derived stem cells (ADSC), cultivated in medium containing AS, maintain characteristics of MSC. The results show that the obtained ADSC were plastic adherent, rapidly dividing (doubling time 40 ± 4 hours), spindle-shaped cells with fibroblastoid morphology and exhibited normal karyotype. No less than 95% of the obtained cells displayed MSC surface markers, including CD73, CD90 and CD105, but showed no expression of the hematopoietic markers CD34 and CD45. ADSC cultured in the presence of AS underwent in vitro differentiation into adipocytes, osteoblasts and chondroblasts, confirmed by Oil Red O, Alizarin Red S and Alcian Blue stains, respectively. These findings suggest that ADSC may be expanded in the AS without the loss of characteristics of MSC.