50 patients with degenerative chondral lesions of the knee cartilage were randomized to determine the effect of stem cells on cartilage repair. Following arthroscopic drilling, patients received hyaluronic acid injections either with or without peripheral blood stem cells, and were evaluated after 18 months. MRI findings at 18 months suggested improved repair in patients treated with the combined stem cell/hyaluronic acid injection. Histologic specimens following 2nd-look arthroscopy and chondral core biopsy were similar to MRI results, indicating improved repair in the intervention group. These findings were not correlated with improved clinical outcomes