The Seanad observed a minute's silence as a mark of respect to the victims of the Madrid bombings.
The Leader of the House, Mrs O'Rourke, who proposed the gesture on behalf of all the parties and groups, said: "We are comrades in Europe and we are comrades in peace. This is a terrible thing to have happened."
The atrocities in the Spanish capital were condemned on all sides ,and a number of members strongly criticised Sinn Féin for inviting representatives of "the political wing of Eta" to the party's ardfheiseanna over the years.
Mr David Norris (Ind) said there were representatives of Sinn Féin with its armed wing, the IRA, in the Dáil.
"I would like very much to hear them condemn their former allies, members of which were honoured guests at a time when they were also committing these atrocities, at their ardfheiseanna," he said.