Blood coagulation and fibrinolysis in pregnancy with or without hyperlipidemia were studied. Blood samples were taken from 36 cases with early pregnancy, 59 cases with late pregnancy, and the relationship between the hemostatic changes and the concentrations of lipids was examined. The following results were obtained: 1. In early pregnancy, all cases were non-hyperlipidemic, but in 41% of late pregnancy cases, hyperlipidemia was found. 2. In late pregnancy without hyperlipidemia, shortening of prothrombin time and activated partial thromboplastin time, increases in platelet epinephrine, collagen aggregation, fibrinogen, and plasminogen, and a decrease in alpha 2-plasmin inhibitor were marked compared with those in early pregnancy without hyperlipidemia. 3. In late pregnancy with hyperlipidemia, the platelet count and fibrinogen were increased, and prothrombin and activated partial thromboplastin time were shortened compared with late pregnancy without hyperlipidemia. The platelet epinephrine aggregation was slightly decreased. Antithrombin III was increased and alpha 2-plasmin inhibitor was slightly decreased. 4. In the same subjects, the relationship between changes in blood coagulation and fibrinolysis in early and late pregnancies and total cholesterol was studied by the independent matched pair test. There were significant correlations (p less than 0.02, p less than 0.05) between activated partial thromboplastin time (r = -0.5998) and fibrinogen (r = 0.6230). From these results the author concluded that late pregnancy was a hypercoagulable state and this tendency was more obvious in late pregnancy with hyperlipidemia.