The effect of increased and decreased uniaxial tissue tension on capillary blood flow, plasma volume, edema formation, and vascular permeability in myocutaneous flaps was studied. A total of 64 equally sized arterialized myocutaneous flaps were outlined on the abdomen of 16 dogs. The four areas on each dog were randomized to either untouched control area, reattachment to normal tension, increased (one and one-half times the original length), or decreased (one-half times the original length). Capillary blood flow measured by the radioactive microsphere technique two hours after operation was decreased in the muscular part of flaps reattached at decreased and normal tension (p less than 0.05). The muscular blood flow was unchanged when flaps were reattached at increased tension and significantly higher than in flaps reattached at decreased tension (p less than 0.05). No differences were found in skin or subcutaneous blood flow. There were no differences in plasma volume, vascular permeability, or total water content between flaps attached under different tensions, whereas the plasma volume was increased in muscle in all three flap types (p less than 0.05) presumably secondary to venous stasis. The study implies that the decreased capillary blood flow seen in the muscular component of a myocutaneous flap in the immediate postoperative period may be counteracted by a somewhat increased reattachment tension.