Provocative pharmacologic testing reliably predicts the safety of arterial embolization. Arteries with intra-axial destinations are tested with a barbiturates and arteries with extra-axial destinations are tested with lidocaine. Testing is quickly and easily performed, essentially risk-free, and reduces the incidence of complications. Despite extensive knowledge of microvascular anatomy, anatomic variations and branches below the limits of angiographic resolution make provocative pharmacologic testing essential to minimize complications during arterial embolization.