It's the preliminary round ahead of a slugfest in November.

Republicans and Democrats go to the polls Saturday to decide who will represent their parties in the November election for one of Louisiana's U.S. Senate seats.

The favorites are Republican incumbent David Vitter and Democratic Congressman Charlie Melancon. Each has drawn a pair of opponents.

Also on the ballot is the Democratic primary for the 4th Congressional District seat in Northwest Louisiana. The winner between Steven Gavi and David Melville takes on incumbent U.S. Rep. John Fleming and the Rev. Artis Cash in November.

Polls will be open from 6 a.m. to 8 p.m. Only Republicans can vote in the Republican Primary; those with no party affiliation can vote in the Democratic or Libertarian Party primaries.

Melancon and Vitter are already running attack ads against each other -- Vitter for his involvement with a prostitute and Melancon over some of his votes in Congress.

But before they get to the main bout in November, there are party primaries.

Vitter has two opponents: retired state Supreme Court Justice Chet Traylor and Nick Accardo. Melancon also has two opponents: Neeson Chauvin and Cary Deaton.

Vitter survived a 2007 prostitution scandal and has shrugged off fresh questions about allowing an aide to remain on his staff after an attack on a woman.

One Melancon attack ad talks about Vitter's phone number in the records of a Washington prostitution ring. It also mentions an aide remaining on staff after he was arrested for attacking the woman in his apartment. The woman's chin and hand were cut but she was not seriously injured. The aide pleaded guilty to misdemeanor charges but wasn't let go until two years later, after an ABC report. Vitter's office said he accepted the aide's resignation after learning of additional legal problems, including a DWI case.

Traylor also has problems stemming from his love life.

His wife, who died last year, was once married to a state lawmaker, with whom she had two sons. Last month, that legislator publicly accused Traylor of helping break up his marriage. The sons are now in a legal fight with Traylor over their mother's estate, and Traylor is romantically involved with the estranged wife of one of the sons.

Taking advantage of President Barack Obama's low popularity in Louisiana, Vitter has linked Melancon to Democratic policies, including the health care overhaul, which Melancon voted against.