The success over the years in reducing inflation and, consequently, the average level of nominal interest rates has increased the likelihood that the nominal policy interest rate may become constrained by the zero lower bound. When that happens, a central bank can no longer stimulate aggregate demand by further interest-rate reductions and must rely on "non-standard" policy alternatives. To assess the potential effectiveness of such policies, we analyze the behavior of selected asset prices over short periods surrounding central bank statements or other types of financial or economic news and estimate "noarbitrage" models of the term structure for the United States and Japan. There is some evidence that central bank communications can help to shape public expectations offuture policy actions and that asset purchases in large volume by a central bank would be able to affect the price or yield of the targeted asset.