The aims of our study were to confirm the effectiveness via animal study and safety through clinical trials of using human cord blood-mononuclear cells (HCB-MNCs).We performed a dose-response animal study (HCB-MNCs: 4 × 10⁶, 4 × 10⁷ and 4 × 10⁸) using a limb ischaemia model in dogs to assess angiogenic responses. Safety assessment in humans in terms of graft-versus-host-disease was also done by observing an uncontrolled case series.Twelve animal ischaemic limbs and seven patients with thromboangiitis obliterans were treated with HCB-MNCs. These cells (4 × 10⁸) were injected into the ischaemic limb muscle of patients. The results were analysed at 8 weeks for the animal study and at 6 months for patients.In the animal ischaemic models, the number of capillaries, angiogenic gene expression and the angiogenic factors were increased after HCB-MNC injection. In the clinical study, the seven patients experienced no graft-versus-host-disease or cardiac/cerebral complications during the follow-up period.This preliminary study suggests that HCB-MNC might be a safe source of stem cells for treating ischaemic limbs. However, further clinical studies are needed to establish the long-term safety and the clinical efficacy of HCB-MNC transplantation in patients with ischaemic limbs.