Support for Sinn Féin has dropped by five points, according to the latest Red C opinion poll for the Sunday Business Post.
The drop brings support for the party back to 13% - the same as it was two months ago - following a surge to 18% in last month's tracking poll.
Support for Fine Gael is unchanged at 31%.
Fianna Fáil is up by one point to 25%, reducing the gap with Fine Gael that was recently as large as 11 points down to six points.
The main beneficiaries of the fall in Sinn Féin's support are other parties on the left - the Social Democrats, the Green Party and Solidarity-People Before Profit - who all see their support rise by a point each.
The Social Democrats and the Greens are now on 3%, while Solidarity-People Before Profit are on 2%. The Independent Alliance are up by a point to 3%.
Support for Independents is unchanged at 15% and Labour unchanged at 5%.
Both Renua and Peadar Tóibín's new party Aontú are on less than 1%.
The Red C telephone poll of 1,000 adults was taken between Thursday 21 March and Thursday 28 March, and has a margin of error of plus or minus 3%.