We used color Doppler ultrasound (US) to study postoperative changes in blood flow in 10 non-innervated free latissimus dorsi (LD) muscle flaps transplanted onto lower extremities. The peak, mean, and minimum velocities, resistance index, and diameter of the pedicle, and the recipient and control arteries were recorded preoperatively and on the 2nd, 5th, and 10th days after surgery. In the pedicle of the transplant, the peak and mean velocities increased but not significantly during the follow-up. The minimum velocity value in the thoraco-dorsal artery was (mean+/-SD) 4+/-5 cm/sec preoperatively, and was in the leg 19+/-9 cm/sec (P < 0.05) on the 5th and 17+/-10 cm/sec (P < 0.05) on the 10th postoperative day. The preoperative value of the resistance index decreased from 0.92+/-0.12 to 0.79+/-0.08 on the 10th postoperative day (P < 0.05). In the recipient artery, the peak (117+/-37) and mean (35+/-16 cm/sec) velocities increased significantly on the 5th postoperative day compared to the preoperative value (79+/-22 and 14+/-6 cm/sec, respectively). The minimum velocity increased but not significantly. The resistance index was preoperatively 1.23+/-0.09 and 0.88+/-0.16 (P < 0.05) on the 10th postoperative day. This prospective clinical study demonstrates that blood flow in the pedicle and in the recipient artery of a free muscle flap increases after surgery. This phenomenon may be due to loss of vascular tone and decreased resistance after denervation. Increased blood flow helps to keep the microanastomosis open and also promotes wound healing.