The Taoiseach has told the Mahon Tribunal he cannot recall how or where he purchased Stg£30,000 in the 1990s.
Mr Ahern says the money was purchased to return to Michael Wall in the event that works did not go ahead on the house he intended purchasing at Beresford Avenue in Dublin.
That version of events was given during a meeting with the tribunal in April. But this afternoon, he said he could not recall buying the sterling.
Tribunal Chair Judge Alan Mahon put it to the Taoiseach that the very act of purchasing that amount of money is something one would be unlikely to forget.
Mr Ahern told the tribunal that he could not be sure whether he purchased the money in one lump or instalments, or even if he carried out the transaction with the bank.
Under further questioning he said that he could have had someone else carry out the transaction for him, as he would have been travelling all over the country at the time on party business.
The Taoiseach was also accused of giving 'polar opposite' accounts of his reasons for withdrawing £50,000 and placing it in a safe at his constituency office.
One of the three judges sitting at the tribunal, Judge Mary Faherty, made the point to the Taoiseach this afternoon.
Earlier today, Mr Ahern had agreed that five cash lodgements made during the 1990s were memorable and all involved foreign exchange transactions.
The four cash lodgements made during a 13-month period in 1994 and 1995 total more than IR£84,000.
Mr Ahern had again insisted that the lodgement of Stg£30,000 made into an account in the name of Celia Larkin in December 1994 was money given by Manchester businessman Michael Wall.
He said the money was used for the renovation of the house, which he intended to rent from Mr Wall at Beresford Avenue.
Mr Ahern says he has evidence to back up his explanation and that an expert witness is available to refute in particular the claim that he lodged any US dollars.
Several times this afternoon members of the public applauded Mr Ahern. They were then reminded by Tribunal Chairperson Judge Alan Mahon that clapping was not allowed.
