Fine Gael remains a point ahead of Fianna Fáil in the latest Sunday Times Behaviour and Attitudes opinion poll.
Amid speculation Taoiseach Enda Kenny will announce next week that he is to step down as party leader, Fine Gael is at 28% - a drop of one point compared with last month.
Fianna Fáil also drops one point to stand at 27%, while support for Sinn Féin is unchanged at 18%.
Labour and the Independent Alliance are both down one point to 4%.
The poll also shows support for the non-aligned Independents increased by 2% to 12%.
The Greens are on 2%, while Solidarity/PBP, the Social Democrats and Renua are all on 1%.
This survey of voters, taken over 13 days up to last Tuesday, has a margin of error of 3.3%.
