Objective: To elucidate the time course and magnitude of hemodynamic and fibrinolytic changes associated with sequential gradient intermittent pneumatic compression (SGIPC), Design: Two-phase, intervention and response investigation in normal volunteers, Materials and Methods: Subjects were assigned to control (phase I) or compression (phase II) groups, Serial blood samples were obtained via femoral venous catheters for tissue plasminogen activator (tPA), plasminogen activator inhibitor (PAI-1), tPA-PAI-1 complex (tPA-PAI), and euglobulin lysis time (ELT) from all subjects and for fibrin degradation products (FbDP) and fibrinogen degradation products (FgDP) from phase II subjects. Duplex venous scanning was carried out on phase II subjects before and during SGIPC, Results: Catheter placement caused elevations in PAI-1 and tPA-PAI, which stabilized within 4 hours of catheter insertion, In phase II, SGIPC induced significant increases in FbDP, FgDP, and tPA-PAI and decreases in ELT and PAI-1, all of which quickly reverted to baseline on termination of compression, Femoral venous blood flow increased by more than 100% with SGIPC, Conclusions: Sequential gradient intermittent pneumatic compression induces prompt, but short-lived, alterations in both fibrinolytic and hemodynamic function, Noncontinuous SGIPC may result in suboptimal thromboembolic prophylaxis.