This study was undertaken to evaluate the effect of ketorolac (Toradol), a potent cyclooxygenase inhibitor used for postoperative pain, on microvascular thrombosis in an established thrombosis model. Bilateral 3-mm arterial inversion grafts (n = 66) were constructed in the femoral arteries of New Zealand White rabbits. ALZET (ALZA Corporation, Palo Alto, Calif.) osmotic pumps were implanted in the external jugular veins for drug delivery. The blinded protocol called for the experimental animals to receive intravenous doses of ketorolac of 1.72 mg/kg per day (group 1) or 3.44 mg/kg per day (group 2), while control animals received equivalent volumes of saline. Patency was assessed at 7 days. Whereas 52 percent (13 of 25) of control vessels remained patent, 70 percent (14 of 20) and 86 percent (18 of 21) of group 1 and group 2 vessels, respectively, were patent at 1 week. This decrease in microvascular thrombosis with delivery of ketorolac was statistically significant (p = 0.0094). Ketorolac, at experimental doses approximating 9 and 18 mg IV q6h in a 70-kg man, demonstrated a statistically significant reduction in microvascular thrombosis. This study supports its use in clinical microvascular surgery.