"Fannie Mae and Freddie Mac are government-sponsored enterprises (GSEs) that purchase mortgages and issue mortgage-backed securities (MBS). In addition, the GSEs are active participants in the primary and secondary mortgage markets on behalf of their own portfolios of MBS. Because these portfolios have grown quite large, portfolio purchases as well as MBS issuance are likely to be important forces in the mortgage market. This paper examines the statistical evidence of a connection between GSE actions and the interest rates paid by mortgage borrowers. We find that both portfolio purchases and MBS issuance have negligible effects on mortgage rate spreads and that purchases are not any more effective than securitization at reducing mortgage interest rate spreads. We also examine the 1998 liquidity crisis and find that GSE portfolio purchases did little to affect interest rates paid by borrowers. These results are robust to alternative assumptions about causality and to model specification"--Federal Reserve Board web site.