Plaid Cymru will consider a change of approach, after it was hit by a double blow in Thursday's general election.
Elfyn Llwyd said lessons needed to be learned
Plaid lost Ceredigion and failed to win its key target of Anglesey, meaning its number of Westminster MPs has fallen from four seats to three.
The defeat follows a poor performance in the 2003 assembly elections when Plaid lost five of its 17 seats.
Plaid Parliamentary leader Elfyn Llwyd said they must find out what has gone wrong and learn from any mistakes.
Mr Llwyd, who held his Meirionnydd Nant Conwy seat, said party chiefs would meet on Monday to discuss the way forward after an "extremely disappointing" poll.
"It is too early to exactly say what has gone wrong, but clearly we must find out what has gone wrong and we must learn from the mistakes, if mistakes there were," he said.
"It has been a bitter blow, but it is a bitter blow we will have to learn from and strengthen our team and our approach and maybe change our approach I don't know.
"A lot of work needs to be done, that will have to start now - we want to obviously do well in the 2007 elections."
Mr Llwyd added that he was disappointed to have lost Simon Thomas in Ceredigion, who was defeated by Lib Dem Mark Williams by 219 votes, and not to have won in Anglesey, which was held by Labour MP Albert Owen.
"If 1,400 votes had gone the other way, we would have won Ynys Mon and held Ceredigion, so it's not an absolute disaster," he said.
"Clearly it's a set back...but it's not half as bad as the media speculation would suggest.
"I increased my majority, Hywel [Williams] in Caernarfon increased his, Adam [Price] increased his dramatically, so we are getting some things right.
Jill Evans said Plaid struggled in a UK context
"We need to be looking at the way in which we have campaigned throughout Wales, we need to be looking at results in every single constituency.
"I am very disappointed but I have been disappointed before and we came stronger out of adversity.
"I am one of those who believes lessons will be learned from this kind of thing.
"I can assure you from Monday morning there will be a lot of talking and discussion."
Plaid MEP Jill Evans added that it was difficult for the party to fight in a UK context.
"We don't get the same media profile as the other parties, but we are looking forward very confidently to the next National Assembly elections," she said.
"We do have a very strong message, we do have a message that does appeal to the people of Wales and we have proved that in the seats we have held."