A group of big US banks has injected $30bn (£24.8bn) into a smaller regional bank, First Republic, which had been seen as at risk of failure.
The move came as authorities in the US are trying to quell panic over the health of the banking system, after a series of bank collapses.
Worries about the sector have spread globally, raising fears of a crisis.
US regulators called the move "most welcome", while the banks said their action reflected their "confidence".
They said the banking system had plenty of cash and made big profits.
"Recent events did nothing to change this," they said. "The actions of America's largest banks reflect their confidence in the country's banking system."
Reports of plans for the aid from the 11 banks, led by JP Morgan and Citigroup, helped lift financial markets and sent shares in First Republic surging more than 20% at one point, triggering trading halts.