Mesenchymal stem cells (MSC) offer great promise in therapies aimed at repairing, replacing or regenerating damaged or diseased tissues and organs. This potential is due to their capacity for self-renewal, ability to differentiate down a range of lineages, and potential in autologous therapies, free from major ethical concerns. This review examines the issues around the use of MSC in tissue engineering (TE) applications. Key issues facing widespread MSC therapeutic use include both the scarcity in adult tissues and the current lack of a simple unambiguous identifying marker. These major challenges facing the isolation, characterization and expansion of MSC to therapeutically significant numbers currently limit their usefulness as 'off the shelf' therapies. Balanced against this, recent evidence suggests that MSC have a much wider tissue distribution and greater plasticity than originally envisaged. Although therapeutic applications of MSC initially focused on mesenchymal lineages such as cartilage and bone, this is now broadening to include organs such as the heart and skin. Ultimately, the clinical utility of such MSC-based therapies will depend on their performance and cost. (c) 2008 Society of Chemical Industry.