Like mesenchymal stem cells from bone marrow (BM-MSCs), adipose tissue-derived adult stem cells (ADAS cells) can differentiate into several lineages and present therapeutical potential for repairing damaged tissues. The use of allogenic stem cells can enlarge their therapeutical interest, provided that the grafted cells could be tolerated. We investigate here, for the first time, the immunosuppressive properties of ADAS cells compared with the well-characterized immunosuppressive properties of BM-MSCs. ADAS cells did not provoke in vitro alloreactivity of incompatible lymphocytes and, moreover, suppressed mixed lymphocyte reaction (MLR) and lymphocyte proliferative response to mitogens. The impairment of inhibition when ADAS cells and BM-MSCs were separated from lymphocytes by a permeable membrane suggests that cell contact is required for a full inhibitory effect. Hepatocyte growth factor is secreted by both stem cells but, similar to interleukin-10 and transforming growth factor-beta (TGF-beta), the levels of which were undetectable in supernatants of MLR inhibited by ADAS cells or BM-MSCs, it did not seem implicated in the stem cell suppressive effect. These findings support that ADAS cells share immunosuppressive properties with BM-MSCs. Therefore, ADAS cell-based reconstructive therapy could employ allogenic cells and because of their immunosuppressive properties, ADAS cells could be an alternative source to BM-MSCs to treat allogenic conflicts.