This study explores the utility of mesenchymal stem cells (MSCs) in a cell therapy approach to intervertebral disc regeneration. We used in vitro and in vivo models to address the issues of exogenous cell delivery, retention, and viability in the pressurized disc space. MSCs in hydrogel carriers of varying viscosity were injected in vitro into a pressurized disc model. Microscopic observation indicated that increasing carrier viscosity was effective at increasing cell retention. In vivo experiments of MSC injection into rat coccygeal discs were performed using 15% hyaluronan gel as a carrier. Injections of gel with or without MSCs were performed. Immediately after injection, fluorescently labeled stem cells were visible on sections of cell-injected discs. Seven and 14 days after injection, stem cells were still present within the disc, but their numbers were significantly lower. At 28 days, a return to the initial number of injected cells was observed, and viability was 100%. A trend of increased disc height compared to blank gel suggests a therapeutic effect. The results indicate that MSCs can maintain viability and proliferate within the rat intervertebral disc