DUP leader Peter Robinson has been admitted to Belfast's Royal Victoria Hospital as a precautionary measure, a hospital spokesman has confirmed.
A spokesman for Mr Robinson said the 66-year-old had a reaction to some medication and was admitted to hospital as a precautionary measure.
The spokesman said Mr Robinson was doing well and would be discharged from hospital soon.
In May Mr Robinson was treated in hospital after suffering a suspected heart attack.
At that time he underwent a procedure.
Mr Robinson stepped aside as first minister in early September after the Ulster Unionist quit the Assembly and the Democratic Unionists pulled four of their five ministers out of the administration.
The resignations came as a result of the PSNI saying current members of the IRA may have been involved in the recent shooting death of Kevin McGuigan and that the paramilitary group still existed.
The controversy escalated when three senior republicans were arrested by detectives investigating the McGuigan murder. All three were later released without charge.
But during the period they were being questioned, Mr Robinson stepped down and three of his DUP ministers quit the Stormont Executive.
Arlene Foster replaced Mr Robinson as first minister on a temporary basis.
Tomorrow the DUP is to join the other parties and the British and Irish governments in talks aimed at breaking the political log jam in Stormont.
Sinn Féin Deputy Leader Mary Lou McDonald has said she hopes talks, aimed at resolving the Stormont crisis, will go ahead tomorrow after Mr Robinson was admitted to hospital.
Speaking on RTÉ's Marian Finuance Show with Aine Lawlor, Ms McDonald said she wished the DUP leader well but hoped the discussions would continue on Monday morning.
She said: "I also hope that we are in a position to meet tomorrow morning and that we are in a position to start talks that have to be about sorting out the issues that we have, making the institutions sustainable and building on the very considerable progress made over the last number of years."
