Graft implantation is one of the more popular procedures for repairing cartilage defects; however, sacrifices of the donor site have been an issue. Mesenchymal stem cells (MSCs) are a fascinating source for regenerative medicine because they can be harvested in a less invasive manner and are easily isolated and expanded, with multi-potentiality including chondrogenesis. MSCs can be isolated from various adult mesenchymal tissues including synovium. Here, we attempted to form cartilage from the composites of synovium-derived MSCs with collagen gel in vitro. After 21 days of culture, the composites had increased their cartilage matrix, as demonstrated by toluidine blue staining and immunohistochemistry for type II collagen. The composites consisting of 5 x 10(7) and 10(8) cells/ml in gel were richer in proteoglycans than those consisting of lower cell densities. After 1 day, MSCs/gel composites contracted and the diameter decreased by 30%; however, they were stable thereafter. Round cells with short processes producing collagen fibrils showing a similar morphology to that of chondrocytes were seen in the composites by transmission electron microscopy. During composite culture, chondroitin sulfate and mRNA expression for cartilage-related genes increased, demonstrating cartilage maturation. Using an optimized method, we obtained cartilage discs with a diameter of 7 mm and a thickness of 500 microm. Our procedure should thus make it possible to produce a large cartilage matrix in vitro. The tissue engineering of autologous cartilage from the composites of synovium-derived MSCs with collagen gel in vitro for transplantation may be a future alternative to graft implantation for patients with cartilage defects.