Objective - To evaluate a surgical technique for performing laparoscopic bilateral ovariectomy in standing horses. Study Design - Experimental study. Animals or Sample population - 8 mares, age 2-20 years, weight 410-540 kg. Methods - Standing laparoscopic bilateral ovariectomy was performed in 8 mares with normal anatomy of the reproductive tract. The Harmonic Scalpel (an ultrasonically activated instrument) was used to transect the ovarian pedicle and to obtain hemostasis simultaneously. Necropsy was performed on 4 mares 3 days after surgery and 30 days following surgery on the remaining 4 mares. Gross and histopathologic evaluation of the ovarian pedicles was performed to characterize the effects of the Harmonic Scalpel on the transected tissue. Results - The Harmonic Scalpel achieved complete hemostasis of the vasculature of the ovarian pedicles in all mares. Median transection time for the ovarian pedicle was 28 minutes. Postoperative complications included transient fever in one mare, moderate subcutaneous emphysema in another, and incisional seroma formation in a third mare. Post-mortem examination 3 and 30 days postoperatively revealed no signs of generalized peritonitis, postoperative hemorrhage or adhesion formation. Mild to moderate acute inflammation, and scar formation with moderate chronic inflammation at the ovarian pedicle was found 3 and 30 days after surgery, respectively. Median depth of coagulation necrosis 3 days postoperatively was 2.87 mm. Conclusions - The Harmonic Scalpel appears to provide reliable hemostasis of the ovarian pedicle during elective laparoscopic ovariectomy in horses. Clinical Relevance - The Harmonic Scalpel represents a safe alternative to other means of hemostasis during elective laparoscopic ovariectomy in horses. / Master of Science