The authors investigated blood coagulation activity in patients who underwent microsurgery. Hemostatic parameters were measured in 9 patients (10 operations) who were undergoing free tissue transfers. These parameters included prothrombin time (PT), activated partial thromboplastin time (APTT), fibrinopeptide A (FPA), prothrombin fragment 1 + 2 (F1 + 2), and thrombin-antithrombin complex (TAT). The flap totally necrosed owing to vasospasm in 1 patient with osteomyelitis of the heel, and the FPA, F1 + 2, and TAT values significantly increased. Reexploration was required because of flap cyanosis in 1 patient with a hemangioma on the wrist, and the F1 + 2 and TAT values increased during the salvage procedure. These molecular markers could be important in indicating hypercoagulable state sensitivity, and they serve as a warning of possible vascular compromise to a surgeon.