In recent years much research has centered upon whether yield differentials between bonds which differ in default risk vary systematically over the business cycle. Theory suggests that during a cyclical upswing the yield differential (or risk premium) narrows, while during a downswing the differential widens. The cyclical behavior of yield spreads is well documented in the corporate bond market [4, 8, 12, 16]. This effect has only recently been given attention in the tax-exempt bond market [1, 11]. In addition, the municipal bond market may be segmented. If tax-exempt borrowers and investors are unable to substitute between tax-exempt securities of varying default risk, changes in the relative supply of and demand for these classes of securities could produce systematic fluctuations in tax-exempt yield differentials. These effects could be produced by regulatory statutes which require that banks purchase high-grade securities and the fixed nature of bond ratings.