Polling stations in South Tipperary reported a 45 per cent turnout this evening, with less than an hour to go before the polling stations close.
It was hoped that the choise of a Saturday wouldencourage a significant proportion of the 55,055 registered voters to go to the 150 polling stations throughout the constituency.
The seat was left vacant by the death of the sitting member of parliament Ms Teresa Ahearn last September.
The poll will be the first electoral test of the opposition Fine Gael leader Mr Michael Noonan, who replaced former party leader Mr John Bruton as head of the party in February.
This is the second by-election to be fought in the South Tipperary constituency in the lifetime of the current Government.
In a by-election, the second preference votes of the defeated candidates, counting the weakest first, are added to the totals until the winner reaches one vote more than half of all votes cast.
Voting takes place between 9 a.m. and 10 p.m. today, with the counting due to start tomorrow morning.
A spokesman for the returning office said the first count results were expected by 2 p.m. and that staff "hope to be finished counting by 4.30 p.m.".
This would allow the electoral team watch the Munster hurling final featuring Tipperary and Limerick at kick-off 4.20 p.m. in Cork.
The candidates are Fine Gael's Senator Tom Hayes, Independent Mr Phil Prendergast, Fiánna Fail’s Mr Michael Maguire of party, and Labour’s Mr Denis Landy.
Additional reporting from PA