John Glenn had to undergo the same type of medical tests that all individuals face before flying into space.

"Essentially the standard is the same irrespective of your age,'' explains Dr. Dave Williams, life sciences director at Johnson Space Center.

NASA's medical requirements differ for each of the three categories of shuttle crew members. Pilot-astronauts, including commanders and shuttle pilots, and mission specialists, who coordinate shuttle operations and perform spacewalks, face more stringent requirements than payload specialists, persons other than NASA astronauts who have specialized onboard duties.

As a payload specialist aboard the shuttle Discovery, Glenn had to pass a series of evaluations of his respiratory, cardiovascular, neurological and gastrointestinal systems. He also had to meet the following requirements: (His results were not available because NASA does not release personal medical data.)

• Distant vision correctable to 20/40 in his best eye.

• Near vision correctable to 20/30 in his best eye.

• Hearing in his best ear at 35 decibels at 500 hertz, 35 decibels at 1,000 hertz and 40 decibels at 2,000 hertz.

• Height between 58 inches and 76 inches.

• Blood pressure less than 140 over 90 with medication allowed.