US Army Sgt. Bowe Bergdahl disappeared from his base on June 30, 2009, and is believed held in Pakistan.
His mother and father issued a statement today saying they've received a letter they are confident was written by their son.
Bob and Jani Bergdahl say the letter, delivered through the International Committee of the Red Cross, gives them hope that their son is doing as well as can be expected, under the circumstances.
They didn't release excerpts from the letter or detail its content.
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They renewed their plea for his captors to release Bergdahl, who turned 27 on March 28.
"We hope Bowe's captors will again consider his parents' plea to release him, but in the meantime, we ask that you please continue to keep him in good health and allow him to keep corresponding with us," they wrote.
Bergdahl's captivity has been marked by only sporadic releases of videos and information about his whereabouts.
Though he's thought by the United States to be held by the Haqqani Network, a Pakistan-based group that President Barack Obama's administration has declared to be a terrorist organization, leaders of the network said in December that Bergdahl was actually being held by another Taliban group.