Ken Maginnis and John Taylor have been crucial figures of support for the Ulster Unionist leader David Trimble.
Both MPs have survived murder attempts by republicans and both have served since 1983 in their present constituencies.
Ken Maginnis has been a strong supporter of the Good Friday Agreement peace accord.
The member for Fermanagh south-Tyrone has steadfastly supported Mr Trimble against increasing pressure from the anti-agreement faction of the party.
He has said his decision to stand down is not connected to political pressures.
In a BBC Radio Ulster interview he said he had worked through "18 years of ups and downs".
"I have seen Ulster Unionism claw its way back to a situation where people have an opportunity to move forward to heal old divisions," he said.
"Quite simply I have done the job at Westminster for 18 years, I have been a school teacher for 24 years before that, I have served in the Ulster Defence Regiment for 12 years and I have run a business," he said.
"I would like to work more to my own schedule than I am able to do as a member of parliament."
As the party's security spokesman, Mr Maginnis is likely to remain a high profile figure as the battles on the reform of policing, demilitarisation and illegally held paramilitary weapons still rages.
" I have seen Ulster Unionism claw its way back to a situation where people have an opportunity to move forward to heal old divisions "
He has been one of the most outspoken opponents of changing the Royal Ulster Constabulary's title and emblems and dismantling the RUC reserve.
He has repeatedly called for stronger action to be taken against the IRA.
It has made a number of attempts to murder him over the years yet he was the first unionist MP to agree to appear on television with Sinn Fein's Gerry Adams.
The move was seen as a breakthrough in relations between republicans and unionists as they moved to a position where they now sit in government at Stormont together.
Downfall of leaders
His colleague John Taylor has held the Strangford seat since 1983.
During a long political career spanning the Troubles, Mr Taylor has played a role in many of the dramas surrounding his party.
His support or otherwise has always been seen as crucial to UUP leader David Trimble in his battle to keep his party together.
His support for Mr Trimble has not been as unequivocal as that of Mr Maginnis but his absence from the anti-Agreement camp is a reassurance in itself given his personal history.
This is because John Taylor played a role in the downfall of two other Ulster Unionist leaders Terence O'Neill and Brian Faulkner in 1969 and 1974.
The wealthy businessman and newspaper owner is regarded as one of Northern Ireland's political mavericks.
He is a great survivor and this was never so dramatically illustrated as by an attempt on his life in 1972.
He was machine-gunned by the Official IRA as he got into his car in Armagh City.
His jawbone was shattered and he had extensive plastic surgery.
Against the odds John Taylor lived.