We determined the following coagulo-fibrinolytic activities in 24 patients with systemic lupus erythematosus (SLE) and 20 healthy adults: prothrombin time (PT), activated partial thromboplastin time (A-PTT), factor VIII: coagulant activity), von Willebrand factor antigen (vWF: Ag), antithrombin-III (AT-III), plasminogen (PLG), alpha 2 plasmin inhibitor (alpha 2 PI), alpha 2-plasmin inhibitor-plasmin complex (PIC), protein C (PC: activity and antigen concentration), and protein S (PS: total PS and free PS). PLG, AT-III, PC antigen concentration and total PS were significantly decreased in ten female controls as compared with ten male controls. Therefore, we used the ten healthy females as controls and excluded two male SLE patients in the analysis of the correlations of coagulo-fibrinolytic activities with lupus anticoagulant (LA), clinical and laboratory features in 22 female patients with SLE. In the SLE patients, PT was significantly shortened, while A-PTT was prolonged. PLG, PC activity and antigen, and total PS were significantly increased, and free PS levels were decreased in SLE. The shortened PT and decreased free PS suggest hypercoagulable states in SLE patients. A significant prolongation of A-PTT and a decrease of F VIII activity were observed in the six LA-positive SLE patients, and the results were considered as known effects of LA. Furthermore, vWF: Ag, AT-III and PC antigen levels were significantly increased in the LA-positive patients as compared with LA-negative patients. These changes indicate both vascular endothelial cell damages and a compensatory increase in coagulation inhibitors in the LA-positive patients.