The fate of Rep. William Jefferson, whose long tenure was threatened by a federal bribery investigation, would be determined Saturday in a runoff that was one of the nation's last unresolved midterm races.
Early returns showed a tight race with fellow Democrat Karen Carter, a state representative.
Jefferson, an eight-term congressman, was in danger of becoming the only Democratic incumbent to lose this election year.
There were more poll workers than voters when Jefferson, Louisiana's first black congressman since Reconstruction, arrived at his polling place with his wife and two daughters on a chilly morning.
Jefferson said he had been worried that overnight temperatures close to freezing might diminish enthusiasm for voting in this normally warm climate. However, temperatures rose into the mid 40s as the sun rose.
He was forced into the runoff against Carter when he failed to win 50 percent of the vote in a crowded open multiparty primary. Carter, 37, is seeking to become the first black woman from Louisiana elected to Congress.
Jefferson, 59, has been handicapped by a wide-ranging investigation into allegations that he took bribes - including $90,000 allegedly found in his freezer during an FBI raid - from a company seeking lucrative contracts in the Nigerian telecommunications market. He has not been charged with any crime and denies any wrongdoing.