In a hypothetical world where deposit-taking banks are the only financial intermediaries, their liabilities as measured by traditional monetary aggregates--such as M2--would be good indicators of the aggregate size of the balance sheets of leveraged institutions. Instead, this paper emphasizes market-based liabilities such as repos and commercial paper as better indicators of credit conditions that influence the economy. The paper concludes that there is a case for rehabilitating a role for balance sheet quantities for the conduct of monetary policy. Results highlight the way that monetary policy and policies toward financial stability are linked. When the financial system as a whole holds long-term, illiquid assets financed by short-term liabilities, any tensions resulting from a sharp pullback in leverage will show up somewhere in the system.