JPMorgan used $17.6 billion, or 16 percent of the total it handled, to purchase debt from money funds run by its own money- management unit, JPMorgan Funds, according to Fed data. BNY Mellon used 89 percent of its $12.9 billion in loans to buy debt from money funds in its Dreyfus unit, the data show. Ron Gruendl, a spokesman for BNY Mellon in New York, declined to comment.

'Breaking the Buck'

AMLF opened for business after investors withdrew $230 billion from money funds in the four days after Lehman's failure. Their withdrawals were accelerated when losses on Lehman debt caused Reserve Primary to drop below $1 a share, an event known as "breaking the buck" that has proved fatal the two times it occurred.

Other funds faced the prospect of having to sell assets at a loss to meet redemptions. Because such funds are the largest collective buyer in the commercial-paper market, their sudden liquidity squeeze also threatened the ability of U.S. companies to sell short-term debt. AMLF helped ease the crisis by lending banks the money to purchase the commercial paper at amortized cost -- the level at which the funds valued the notes -- from the funds that most needed cash.

'Restoring Liquidity'

"AMLF was critical in restoring liquidity and confidence to the commercial-paper market," Brian Reid, chief economist of the Investment Company Institute, a Washington-based trade group for the funds industry, said in an e-mail. "Money-market funds turned from net sellers of commercial paper into net buyers after the Fed launched the program."

Only asset-backed debt issued by a U.S.-based borrower with maturities shorter than 120 days for bank holding companies and 270 days for depository institutions was eligible for the program. The securities were also required to carry a rating of at least A1, P1 or F1, the highest ratings for short-term debt, without a "negative watch" designation. The debt could be purchased only from funds experiencing net redemptions exceeding 5 percent of assets in a single day, or 10 percent over 5 consecutive business days.

James Nolan, head of supervision, regulation and credit at the Federal Reserve Bank of Boston, which administered AMLF, said the requirements created at least some risk for banks. Those that chose to participate operated under tight deadlines to ensure the paper they bought complied. They'd have borne any losses on non-qualifying debt, Nolan said.

Outside Normal Business

"We were asking them to do something their normal business doesn't require them to do, and to assume the risk of loss if they failed to comply with the program requirements," he said.

Nathan Flanders, managing director of the fund and asset management ratings group at Fitch Ratings in New York, called the task of meeting the Fed's restrictions "straightforward."