This fall's major-party matchups in Maryland's eight U.S. House districts are all but set, based on the latest unofficial primary returns from the Maryland Board of Elections, with few, if any, changes expected in the state's congressional lineup.

None of the incumbents was seriously challenged in the primary. Rep. Roscoe Bartlett was the only representative to receive less than 70 percent of the primary vote. He got 69.8 percent, compared with 78 percent in the Republican primary two years ago.

In the First District, which takes in the entire Eastern Shore and portions of Baltimore, Harford and Anne Arundel counties, incumbent Democratic Rep. Frank Kratovil of Stevensville will face Republican state Sen. Andy Harris in a rematch of the closest House election in the state two years ago. This is the only House seat in Maryland regarded as a potential party switch in the 2010 midterm.

In the weirdly shaped Second District, which includes portions of Baltimore City, Baltimore and Anne Arundel counties and a number of key installations, including the Port of Baltimore, incumbent Democratic Rep. C. A. Dutch Ruppersberger of Cockeysville will be opposed by Republican Marcelo Cardarelli, a surgeon with a degree in public health from Johns Hopkins.

Third District Congressman John Sarbanes of Towson, whose district includes Baltimore City and Baltimore and Anne Arundel counties, will be challenged by Republican Jim Wilhelm, a technology consultant and Naval Academy graduate.

In the Fourth District, a suburban Washington jurisdiction split between Prince George's and Montgomery counties, incumbent Democratic Rep. Donna Edwards, who lives at National Harbor, will face Republican computer programmer Ralph Broadus, another Naval Academy grad.

In southern Maryland's Fifth District, Congressman Steny Hoyer of Mechanicsville, the House Democratic leader, will be opposed by Republican business executive Charles Lollar.

In the Sixth District, which stretches from northern Harford and Baltimore Counties to the West Virginia line, Bartlett of Frederick, the state's lone Republican in Congress, faces a rematch with a Democrat he defeated in 2006, Army veteran Andrew Duck.

Democratic Rep. Elijah E. Cummings of Baltimore, whose Seventh District includes the city and portions of Howard and Baltimore counties, will be challenged by Frank Mirabile, Jr., a landscape designer and member of a Howard County land use task force.

Democratic Rep. Chris Van Hollen of Kensington will apparently face management consultant Michael Lee Philips in the Eighth District, which includes Montgomery and Prince George's counties. Philips was narrowly leading lawyer Bruce Stern by just 51 votes.

None of the incumbents appears to be seriously threatened, with the exception of Kratovil, who will likely face one of the toughest re-election fights in the country this fall.