Prince Phillip enters hospital
Prince Philip was taken to the King Edward VII's Hospital in London for "assessment and treatment for a chest infection", a palace spokeswoman said.
"His Royal Highness's programme of engagements for the weekend has been cancelled," she added.
The duke, 86, had missed the service of thanksgiving for Everest conqueror Sir Edmund Hillary on Wednesday.
BBC royal correspondent Daniela Relph said the duke was said to be, "up and about and dealing with his correspondence".
Earlier this week Buckingham Palace had said he had a "heavy cold" and had asked for some engagements to be cancelled.
His last official public role was during President Nicolas Sarkozy's state visit to Britain last week.
He walked into the private central London hospital on late Thursday afternoon for tests.