An AIB official has told the Mahon Tribunal that cash lodged at the bank by Taoiseach Bertie Ahern's former partner Celia Larkin in December 1994 was "probably dollars" and not sterling as Mr Ahern previously suggested.
The Taoiseach has previously told the tribunal that the sum, which was worth almost IR £29,000 , was made up mostly of sterling.
Mr Ahern has also claimed several times that he never dealt in dollars.
Celia Larkin told the tribunal through her solicitor that Bertie Ahern asked her to collect a briefcase from his St Luke's office and lodge it to her account at AIB O'Connell Street, which she did on December 5, 1994.
The Taoiseach claims his then landlord Michael Wall gave him the money for the refurbishment of his rented house.
AIB official Rosemary Murtagh has been questioned extensively about the exchange rates and remit rates at the bank on that day.
She has agreed with the tribunal, that following a process of elimination, no possible sterling combination could have produced the figure of IR £28,772.90, and that therefore the money lodged was "probably $45,000".