Hip arthroplasty is associated with a high frequency of postoperative solitary proximal deep vein thrombosis which seems most frequently observed when bone cement is used for prosthesis fixation. Eighteen pigs underwent hemiarthroplasty, eight with cement-fixed prostheses and eight with non-cement prosthesis installation. Levels of thrombin-antithrombin (TAT) complexes, tissue plasminogen activator (t-PA) activity and plasminogen activator inhibitor 1 (PAI-1) activity were determined in femoral vein blood from both limbs during and after surgery. On the operated side, TAT increased during bone traumatization followed by a substantial rise in t-PA activity and a gradual decline in PAI-1 activity. This indicates a local per- and post-operative sequential activation of coagulation and fibrinolysis followed by a fibrinolytic shutdown, all reflected in femoral vein blood on the operated side. In the animals receiving noncemented hip prostheses, the same pattern of activation of coagulation and fibrinolysis occurred on the operated side. This was, however, less marked than with the cement-fixed prostheses. Postoperative scanning electron microscopic (SEM) examination of the femoral veins showed thrombi on the operated side in 62% of the animals in the cement group and 25% in the non-cement group. In an additional study with eight animals undergoing cement-anchored hip prosthesis operations the levels of TAT, t-PA and PAI-I were analysed in femoral vein blood, mixed venous blood and arterial blood. Significantly higher levels were found in femoral vein blood compared with mixed venous blood while no significant change was found in arterial blood compared with mixed venous blood. The hyperthermia induced by curing bone cement was effectively conducted by the implanted prosthesis and did not seem to exert major influence on the activation of coagulation. Extreme rotation of the limbs during surgery did not in itself induce visible vein wall damage as judged by SEM. These studies indicate that traumatization of bone marrow during hip surgery induce a marked local activation of coagulation and a high incidence of deep vein thrombosis in proximal veins, in particular if bone cement is used for prosthesis fixation.