Independent TD Michael Healy-Rae was removed by ambulance from Leinster House after taking ill today.
The Kerry South TD had earlier been severely critical of the welfare cuts during the Dáil debate on the Social Welfare Bill.
He later returned for a vote, but colleagues urged him to leave when it was clear he was unwell.
It is understood he was attended to by Health Minister Dr James Reilly outside the chamber.
He was taken to St James's Hospital.
Mr Healy-Rae holds the seat vacated by his father, Jackie, in the General Election last February.
When Mr Healy-Rae's office was contacted, his sister said the deputy is fine, and is undergoing tests in St James's Hospital.