Democratic Sen. Tim Johnson said Friday that he will run for re-election next year as he continues his recovery from a life-threatening brain hemorrhage.

Johnson's announcement is good news for his party, because prominent Republicans have shied away from the idea of challenging the South Dakota Democrat after his illness and long recovery were closely watched in the state.

"After months of rehabilitation and recovery, more than a month on the job in Washington and after my recent trips back to South Dakota it is clear, to my family, my doctors, and me that I am able to do the hard work required of a United States senator," Johnson said in a campaign e-mail.

Johnson is still undergoing physical speech and physical therapy to address lingering effects of his hemorrhage. His right side is weak, and he uses a motorized wheelchair to get around the Senate.

Five Republican senators have said they will retire next year, giving Democrats an opportunity to expand the narrow majority they won in the 2008 elections. No Democrats have announced plans to retire from the Senate.

Johnson was considered a top Republican target before he fell ill. He won re-election against Republican John Thune in 2002 by just 524 votes, and Thune defeated Democratic Sen. Tom Daschle in another close race two years later.

Despite a nine-month absence from the Senate after his Dec. 13 brain hemorrhage, Johnson has more than $2 million in the bank for his campaign. Several of his colleagues held fundraisers for him while he was recovering.

Two Republicans have said they will seek Johnson's seat: state Rep. Joel Dykstra and Sam Kephart, a self-employed businessman.

Johnson, 60, was rushed to the hospital from his Senate office in December after becoming disoriented on a conference call with reporters. He underwent emergency surgery for arteriovenous malformation, a condition that causes arteries and veins in the brain to grow abnormally large, become tangled and sometimes burst.