Bush, 88, has been hospitalized at Houston's Methodist Hospital for six days and has a "lingering cough," spokesman Jim McGrath told CNN.
"President Bush has been in and out of The Methodist Hospital in the Texas Medical Center being treated for complications related to his bronchitis," his office said in a statement distributed by the hospital. "He is in stable condition, and is expected to be released within the next 72 hours."
Bush has a form of Parkinson's disease that affects his legs and requires him to use a wheelchair.
He is the oldest living former president and a World War II veteran.