A 5-year-old German Warmblood stallion with chronic lameness, attributable to degenerative joint disease(DJD) of the pastern joint unresponsive to medical treatments, was treated with autologous mesenchymalstem cells (MSC). These MSC were isolated from the peripheral blood (PB) of the patient and injected intothe pastern joint, at a concentration of 2.5x106 cells, twice with an 8-week interval. The positive response tothis stem cell treatment was documented by visual gait evaluation as well as objective pressure plate analyses.This paper is the first to describe the use of autologous PB-derived MSC to treat a horse suffering from chronicDJD. The favorable outcome of this single case may stimulate further research on the use of equine peripheralblood as a source of autologous MSC in equine regenerative medicine.