The referendum on Oireachtas inquiries has been rejected by voters by a margin of more than 100,000 votes.
Earlier, the referendum on judicial pay, which proposed to allow Governments to reduce the pay of judges in line with that of other public servants, was passed by a four to one margin.
The highest vote against the measure came in Dublin South East, where 28.5% opposed it; at the other end of the scale was Carlow Kilkenny, where just 17.9% were against.
A close result had been expected in the vote on Oireachtas inquiries; in the end there was a margin of 116,000 votes, as the proposal was defeated by 53.3% to 46.7%.
Only two constituencies supported the proposal; the Taoiseach's Mayo base, with 50.4% in favour, and Wexford, the home of sponsoring Minister Brendan Howlin, where 50.1% supported it.
The highest vote against was in Dublin South East, where 62.9% were opposed.
In a statement Taoiseach Enda Kenny welcomed the passing of the referendum on judges' pay but said it was disappointing that the amendment on Oireachtas inquiries was defeated.
However he added that "the Constitution is something that belongs to the people and we acknowledge and accept the people's democratic decision."
Mr Kenny said the Government will now "reflect and carefully consider the outcome of this referendum".
Meanwhile the Irish Council of Civil Liberties, which campaigned against the amendment, welcomed the result and said it looked forward to participating in consultations on future amendment proposals.