We studied the relationship between vascular complications and coagulation and fibrinolysis parameters in 75 subjects with collagen diseases. Thirty normal healthy persons served as controls. We found that patients with collagen diseases were in a state of a hypercoagulation and hyperfibrinolysis. In SLE (systemic lupus erythematosus) in particular, coagulation and fibrinolysis parameters appeared to be indices of vascular complications. Increases in the levels of thrombin-antithrombin III complex (TAT) and alpha 2-plasmin inhibitor-plasmin (PIP) were particularly associated with proteinuria, while increases in fibrinopeptide A (FPA) levels were associated with Raynaud's phenomenon. Administration of glucocorticoid seemed to improve the hypercoagulation and hyperfibrinolytic states of patients with collagen diseases. Analysis of the multimeric structure of von Willebrand factor (vWF) revealed a tendency for large and intermediate multimers (LIM) of plasma vWF to increase in SLE patients with accompanying vascular complications, whereas such increases were not observed in SLE patients without any vascular complications. Therefore, analysis of the multimeric structure of vWF appeared to be a useful indicator of vascular complications in collagen diseases.