To achieve adequate tissue perfusion during regional isolated perfusion, hind limbs of dogs were perfused for 60 min, regulating the extracorporeal circuit on pressure. The dogs were divided into three groups. In groups I and II perfusions were performed at a delta pressure (systemic mean arterial pressure minus hind limb mean arterial pressure) of respectively 50 and 15 mm Hg; in group III delta pressure was also 15 mm Hg but the cytostatic drug Melphalan was added. Tissue perfusion was determined by means of a multiwire polarographic oxygen electrode. Adequate tissue perfusion was obtained only at subnormal perfusion pressures (groups II and III), although in all groups perfusion flow was higher than preoperative flow. At low perfusion pressures (group I), tissue perfusion was severely impaired. In all groups leakage remained less than 10%. During regional isolated perfusion the extracorporeal circuit must be regulated at a delta pressure of 15 mm Hg to achieve adequate tissue perfusion.