Objective-To investigate the hemostatic response to surgery and compare the response for ovariohysterectomy with that for ovariectomy and to evaluate the usefulness of thromboelastography on plasma samples. Animals-42 female dogs. Procedures-Dogs were assigned to undergo ovariohysterectomy or ovariectomy. Blood samples were collected immediately before and 1, 6, and 24 hours after surgery and stored at -80°C for subsequent analysis. Plasma samples were subjected to thromboelastography after thawing. In addition, coagulation variables were measured, including concentrations of von Willebrand factor antigen, fibrinogen, antithrombin, and protein C; activity of factor VIII; activated partial thromboplastin time; prothrombin time; and thrombin time. The fibrinolytic response was assessed via concentrations of D-dimer, plasminogen, and α-2-antiplasmin (plasmin inhibitor). Results-Substantial hemostatic and fibrinolytic activation was evident after surgery in both groups, as characterized by significantly increased global clot strength and an overall hypercoagulable state at 4 hours after surgery in addition to decreases in von Willebrand factor antigen and factor VIII concentrations and shortened prothrombin and thrombin times. The dogs also typically had activation of the fibrinolytic system, as evidenced by increased postoperative concentrations of D-dimer, plasminogen, and plasmin inhibitor. Differences between the 2 groups could not be detected for any variables. Conclusions and Clinical Relevance-Elective surgery with limited tissue trauma induced hemostatic activation in dogs, which led to hypercoagulability after surgery. A difference between the ovariohysterectomy and ovariectomy groups was not detected. Thromboelastography can be used on plasma samples and may be useful for evaluating patterns over time.