This paper, originally released in August 1989 as part of a Federal Reserve Bank of New York series on the U.S. securities markets, examines loans of Treasury and agency securities in the domestic market. It highlights some important institutional characteristics of securities loan transactions, in particular the common use of agents to arrange the terms of the loans. While we note that this characteristic sets securities lending apart from most repurchase agreement (repo) transactions, which occur bilaterally between a borrower and a lender, we observe that repo and securities loan transactions ultimately serve the same important economic purpose - to cover short positions used for hedging or arbitrage in related cash markets. The data used here, though largely informal, were provided by knowledgeable market participants.