The Duke, who was admitted to hospital yesterday, is likely to remain in hospital for "a few more days", according to official sources.
The Duke, who is 91, was driven 50 miles in an ambulance to Aberdeen Royal Infirmary after feeling unwell during his annual summer break at Balmoral.
This morning, Buckingham Palace said he was undergoing investigation and treatment for the recurring bladder infection, which he also suffered during the Queen's Diamond Jubilee celebrations in June.
An official statement released this afternoon confirms: "The Duke of Edinburgh is responding well to treatment.
"It is unclear when he will be discharged, but he is likely to remain in hospital for a few more days."