Two people familiar with the situation said Biden was being evaluated Tuesday at the University of Texas MD Anderson Cancer Center, one of the leading cancer centers in the nation. The people spoke to The Associated Press on condition of anonymity because they were not authorized to speak in an official capacity.
Biden's wife and other family members, including the vice president, were with him. The vice president's office said he planned to remain in Houston on Wednesday. A hospital spokeswoman said she did not have any information.
Beau Biden, who suffered a mild stroke in 2010, felt weak and disoriented on the night of Aug. 14 after driving to Indiana for a family vacation, said Jason Miller, a spokesman for the Delaware Department of Justice.
Biden, 44, was initially admitted to Northwestern Memorial Hospital in Chicago and traveled the next day to a Philadelphia hospital to consult with his doctor. He was discharged and spent last weekend at home in Wilmington.
The younger Biden posted a smiling photo of his wife Hallie and himself to his Twitter account Tuesday morning.
"Touched by all your well wishes--thank you. Nice evening in Houston w/ Hallie; will share update when we have it," the tweet read.
Miller said Monday night that Biden was undergoing testing in Houston to determine the cause of his symptoms, though he'd declined to say exactly where the testing was being done.
In Washington, White House spokesman Josh Earnest said President Barack Obama spoke by phone over the weekend with Joe Biden to offer his best wishes for the family.
"A lot of people all across the country woke up with Beau Biden on their minds," Earnest said.
The White House said the vice president had been home in Delaware for the past several days before accompanying his son to Houston. It's not clear how long the vice president will stay. He had been scheduled to join Obama in Scranton, Pa., later this week during Obama's two-day bus tour.
The younger Biden's Twitter account on Sunday posted a photo of him and his father sitting on a porch and smiling while sending a message of encouragement to a Delaware team that was in the Little League World Series.
This isn't the first health scare for Beau Biden, who became Delaware's attorney general in 2007. After a mild stroke in May 2010, he spent a week in the hospital and more than a month recuperating at home.
"Stroke was the farthest thing from my mind when I went in," Biden said at that time.
Biden's father has had health scares of his own, including a life-threatening brain aneurysm in 1988, when he was 45.