The poll forecast that, for the first time in its history, the party would drop to second place behind John Hume's nationalist SDLP. This would cause a major upset in that it would put Mr Hume in line for the new post of first minister in the assembly.
Even more worryingly for pro-assembly elements, the poll, conducted for the Irish radio and television service RTE, showed Mr Trimble only one point ahead of the Rev Ian Paisley's Democratic Unionist party.
With Mr Paisley firmly against the Good Friday agreement on which the structure of the assembly is based, such a result would destabilise the new institution. A strong element of anti-agreement Unionists could effectively sabotage some of its workings. A similar exit poll taken at last month's referendums on the Good Friday agreement proved remarkably accurate.
In spite of an exceptionally low-key campaign, turnout appeared to be high yesterday.
Counting starts this morning, with results expected from early afternoon. The count may go into a second day, given that the proportional representation system of voting means a longer tallying process than the Westminster first-past-the-post system.
Heavy mid-afternoon rain in Belfast deterred some voters, but the usual post-teatime rush saw steady streams of voters at the 1,228 polling stations.
In Protestant east Belfast some polling stations were heavily bedecked with multi-coloured election posters, reflecting the keen contest for votes among different shades of Unionist parties in the area.
Over in west Belfast, meanwhile, posters and other decorations exhorting support for Gerry Adams and other Sinn Fein candidates dominated most of the stations.
Almost 300 candidates are seeking the 108 assembly seats, six of which will come from each of the 18 Westminster constituencies. The assembly is expected to meet for the first time on Wednesday of next week to elect a Speaker. Its timetable after that is unclear.
New last-minute polling arrangements were put in place in the Co Armagh village of Newtownhamilton, whose centre was badly damaged by an INLA car-bomb attack on Wednesday.
t The Tories have made a private offer to Mo Mowlam, the Secretary of State for Northern Ireland, to change the Government's Bill to allow the release of prisoners, writes Colin Brown.
Their amendment would harden the Bill by requiring the Secretary of State to "take into account" terrorist activity before releasing prisoners. She would have to make sure their organisations were co-operating with the arms decommissioning body. The Tories, criticised after voting against the third reading of the Bill, could use their strength in the Lords to defeat the Government, if it rejects their move to reinforce the linking of prisoner releases with the decommissioning of weapons.Reuse content