Leno left his office at NBC's Burbank studios and went to the hospital for observation about midday, his spokesman, Dick Guttman, told the Associated Press. The nature of his illness was not released.
NBC released this statement regarding Leno's condition: "Jay Leno is doing just fine. He was kidding around with the hospital staff and running his monologue jokes by the doctors and the nurses. He's expected back to work on Monday."
Ryan Reynolds, Big Bad Voodoo Daddy and wildlife expert Jules Sylvester had been scheduled for Thursday's show. A repeat episode was set to air in its place.
Leno will wrap up his hosting duties on May 29 before he turns over the reins to Conan O'Brien. NBC has carved out a new 10 pm prime-time slot for Leno in the fall.