Introduction) Free flap using microvascular technique has been firmly established since its introduction more than three decades ago. Although the recipient vessels are considered to largely affect the hemodynamics in the transferred tissue, little is known about the physiological alterations among different recipient sites. Currently, we have developed a novel method for monitoring of free flap, which allowed us continuous measurements of vascular pressure within the transferred tissue. This study addressed to elucidate the different hemodynamic alterations in the transferred tissue according to the recipient site. Materials and Methods) Forty-seven cases who underwent free tissue transfer were subjected to this study. All cases received in-situ venous catheterization for monitoring of anastomotic failure. Of these, 25 cases and 21 cases received further monitoring devices for arterial pressure and surface blood flow, respectively. The postoperative monitoring was continued for three days, and all parameters were continuously recorded via a data acquisition system (PowerLab). The cases were divided into three groups depending on the recipient sites, head and neck (N=23), trunk (N=11) and lower extremity (N=14). Results) The venous pressure on the first postoperative day was significantly higher in the lower extremities comparing with that in other parts of the body (lower extremity;28.6±3.0mmHg, head and neck; 12.5±1.7mmHg, trunk;18.5±2.0mmHg). On the other hand, the arterial pressure on the first postoperative day was lower in the lower extremities (lower extremity;76.9±4.6 mmHg, Head and Neck; 93.0±3.4 mmHg, trunk;87.6±5.6 mmHg), although it did not reach to a statistically significance. Therefore, the arterio-venous pressure gradient that is interpreted as a driving pressure perfusing the transferred tissue was significantly smaller in the lower extremities. This smaller driving pressure in the free flap to the lower extremities gradually increased (48.3±5.8, 59.4±4.4 and 63.5±4.4 mmHg on the first, second and third postoperative day, respectively), associated with increase in surface blood flow. The driving pressures in the free flap to the other parts were virtually unchanged during a three-day postoperative period. Discussion) Despite increased successful rate of free tissue transfer approaching more than 95%, that applied to the traumatized lower extremities has specifically higher incidence of vascular thrombosis. The smaller driving pressure might be related to the reported high incidence of complications after free tissue transfer to the lower extremities. Conclusion) Hemodynamics in the free flap is different depending on the recipient sites.