Relatively little is known about the relationship between taxes and asset prices. Differential tax treatment of assets in the same risk class implies differential pricing. Conversely, the ability of tax-exempt investors to engage in tax arbitrage should drive any pricing differences away. The differential tax treatment of classes of US Treasury securities provides a straightforward setting for the examination of possible tax-effects in asset prices. Using the Cox-Ingersoll-Ross Term Structure Model as our framework, we examine the pricing of US Treasury securities over two distinct tax regimes. Evidence that tax effects are not arbitraged away is presented.