The Pope spent a peaceful night in hospital and ate breakfast this morning, the Vatican said.
It comes after it cancelled the Pope‘s weekend engagements after he was diagnosed with bilateral pneumonia.
The 88-year-old, who as a young adult developed a case of pleurisy and had part of one of his lungs removed, has been in Rome‘s Gemelli hospital since Friday for bronchitis treatment.
The Vatican said tests, X-rays and the Pope’s clinical condition continued to present “a complex picture”.
Bronchitis can lead to pneumonia – a more serious infection of the lungs’ air sacs.
Matteo Bruni, director of the Holy See press office, said Pope Francis was in good spirits and was grateful for people’s prayers.
The Pope is said to have been reading newspapers and doing some work from his hospital room during his stay.
Concerns have been growing about the pontiff’s increasingly frail health.
Francis, who has been pontiff since 2013, has had influenza and other health problems several times over the past two years.
Pilgrims arriving at the Vatican this week have offered their prayers that the Pope would recover soon.
Bilateral pneumonia is a serious condition which can affect breathing, after causing inflammation and scarring of the lungs.
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The Vatican has so far not given any indication of how long the Pope will have to stay in hospital.
A spokesperson said the clinical picture had required several changes in his drug regimen and he would require an “adequate” stay.