Greece's biggest lender National Bank on Friday said it had posted a nine-month loss of 2.45 billion euros ($3.2 billion) while number two Alpha Bank said it had lost 711.8 million euros over the same period.
Both banks said they had taken a hit after participating in Greek sovereign debt reduction operations this year, and called for additional recapitalisation funds of 2.3 billion and 1.6 billion euros, respectively.
NBG's operating income dropped 10 percent to 3.03 billion euros in the first nine months of the year, with operating costs down three percent to 1.7 billion.
Alpha Bank's takings fell by 38.2 percent to 1.07 billion while expenses were reduced by 5.6 percent to 785.7 million euros.
Greece's main banks are to receive 50 billion euros overall to restore their capital after a sovereign debt write-down in the spring, and a subsequent debt buy-back earlier this month.
An initial payment was carried out in May and another 16 billion euros in EU rescue money earmarked for the recapitalisation was disbursed on Wednesday.
The country's third and fourth-largest lenders had also reported major losses a day earlier.
Third-ranked Eurobank -- which is due to merge with National Bank -- reported a net loss of 1.095 billion euros ($1.44 billion) and said it would need recapitalisation funds of 5.8 billion euros overall.
Piraeus Bank, fourth overall, said it had lost 629 million euros over the same period and had required a 7.3-billion-euro boost in total.
Eurobank had received a first instalment of 3.97 billion euros for this purpose in May, while Piraeus Bank had drawn 4.7 billion euros.
National Bank picked up 7.4 billion euros seven months ago and Alpha Bank has already received 2.9 billion euros.
European leaders last week decided to unblock a total of 49.1 billion euros from Greece's outstanding financial assistance package by early next year in return for a new austerity deal in Athens.
The release of the money after six months brought a welcome respite to the country's recession gloom.
Ratings agency Standard and Poor's this week gave Greece's sovereign debt a six-point grade increase, and the European Central Bank said it would again accept Greek bonds as collateral for central bank loans.
But the cheer did not extend to Greek banks.
On Thursday, S&P said it was keeping all four main lenders on a triple-C long-term rating.
"Although we believe that sovereign credit-worthiness benefits from the strong determination of the eurozone to restore Greek economic stability and preserve its eurozone membership, we believe that the four Greek banks we rate are likely to continue facing significant risks to their weak financial profiles," the ratings agency said.