Primary voters in Indiana's two most-solidly Republican congressional districts have long lists of choices for whom they want to send to Congress.

In the 5th District, they'll decide whether to pick Rep. Dan Burton for what would make 30 years in Congress. In the neighboring 4th District, the likely replacement for retiring Rep. Steve Buyer will be determined.

Also at stake across the state:

— The re-election bid of GOP Rep. Mark Souder in northeastern Indiana's 3rd District, where he's faced a nasty campaign against an auto dealer with deep pockets.

— The potential for a fifth Baron Hill-Mike Sodrel matchup come November in southern Indiana's 9th District.

— The strength of the Republican nominee in southwestern Indiana's 8th District, where the GOP hopes to win the seat being vacated by Democratic Rep. Brad Ellsworth, who is running for the Senate.

Burton, Indiana's current longest-serving congressman, faces six challengers who have argued it's time for him to go. His opponents include physician John McGoff, who received 45 percent of the vote in a narrow 2008 primary loss to Burton; former state Rep. Luke Messer, who has strong ties with many state GOP leaders; and 16-year state Rep. Mike Murphy.

The race for Buyer's seat has been a three-month sprint after he announced in late January that he would retire after 18 years in Congress because his wife has been diagnosed with an incurable autoimmune disease. Secretary of State Todd Rokita and state Sens. Brandt Hershman and Mike Young are among 13 candidates in the heavily Republican district.

In the 3rd District, challenger and car dealer Bob Thomas has portrayed Souder as a career politician who isn't a true fiscal conservative. Thomas' ads show Souder's picture next to images of Democratic House Speaker Nancy Pelosi and Senate Majority Leader Harry Reid.

Souder, who was first elected in 1994, scoffs at the idea of being anything but conservative. His ads emphasize his A-plus rating from the NRA and a National Right to Life Committee rating of 100 percent.

Former Fort Wayne City Councilman Tom Hayhurst, who gave Souder a stiff challenge in 2006, is the likely Democratic nominee.

The Republican campaign in the 9th District has focused on whether Sodrel should get a fifth shot at Hill, the Democratic incumbent.

Hill and Sodrel have faced each other in each congressional election since 2002. Sodrel won the seat in 2004, but Hill recaptured it two years later and won the 2008 election with nearly 58 percent of the vote.

Attorney Todd Young of Bloomington has run a well-financed campaign for the nomination, while real-estate investor Travis Hankins of Columbus has sought religious conservative voters who previously have backed Sodrel, the founder of a Jeffersonville-based bus and trucking company that made him a multimillionaire.

Eight Republicans are on the primary ballot for the seat now held by Ellsworth, who was considered a strong favorite for re-election before deciding to seek the Senate seat being vacated by Evan Bayh.

Heart surgeon Larry Bucshon of Newburgh has been backed by national Republicans but opposed by some tea party activists because of those ties. State Rep. Trent Van Haaften is unopposed for the Democratic bid.

State Rep. Jackie Walorski has received strong backing in her bid for the Republican nomination against Democratic Rep. Joe Donnelly to set up a potentially bruising campaign for northern Indiana's 2nd District seat.

Only little-known challengers are on either party's ballot against Rep. Mike Pence, the third-ranking Republican in the U.S. House, and Democratic Reps. Pete Visclosky and Andre Carson.