Objectives: The safety and efficacy of direct intramuscular injections of aldehyde dehydrogenase bright (ALDHbr) cells isolated from autologous bone marrow mononuclear cells (ABMMNCs) and ABMMNCs were studied in patients with critical limb ischemia (CLI) who were not eligible for percutaneous or surgical revascularization. Background: Many CLI patients are not candidates for current revascularization procedures, and amputation rates are high in these patients. Cell therapy may be a viable option for CLI patients. Methods: Safety was the primary objective and was evaluated by occurrence of adverse events. Efficacy, the secondary objective, was evaluated by assessment of Rutherford category, ankle-brachial index (ABI), transcutaneous partial pressure of oxygen (TcPO2), quality of life, and pain. Results: ALDHbr cells and ABMMNCs were successfully administered to all patients. No therapy-related serious adverse events occurred. Patients treated with ALDHbr cells (n = 11) showed significant improvements in Rutherford category from baseline to 12 weeks (mean, 4.09 ± 0.30 to 3.46 ± 1.04; P = 0.05) and in ABI at 6 (mean, 0.22 ± 0.19 to 0.30 ± 0.24; P = 0.02), and 12 weeks (mean, 0.36 ± 0.18; P = 0.03) compared with baseline. Patients in the ABMMNC group (n = 10) showed no significant improvements at 6 or 12 weeks in Rutherford category but did show improvement in ABI from baseline to 12 weeks (0.38 ± 0.06 to 0.52 ± 0.16; P = 0.03). No significant changes from baseline were noted in ischemic ulcer grade or TcPO2 in either group. Conclusions: Administration of autologous ALDHbr cells appears to be safe and warrants further study in patients with CLI. © 2011 Wiley Periodicals, Inc.