Pope Francis spent a calm night in hospital after being admitted for a respiratory infection and is expected to remain there for a few days for treatment, a Vatican source has said.
Italian news agency Ansa reported nurses were optimistic he would be out of hospital in time for Palm Sunday this weekend.
It added tests had ruled out heart problems and pneumonia.
The 86-year-old pontiff entered hospital on Wednesday.
In a statement, the Vatican said said Pope Francis had a respiratory infection and would need to remain there for a few days.
The 86-year-old has had breathing difficulties in recent days, but does not have Covid, its statement said.
"Pope Francis is touched by the many messages received and expresses his gratitude for the closeness and prayer," the statement added.
His closest staff, including security, spent the night at the Gemelli Hospital, a person with direct knowledge told the BBC.
This is the busiest time of the year for Pope Francis, with many events and services scheduled ahead of Easter weekend.
A Palm Sunday Mass is scheduled this weekend, with Holy Week and Easter celebrations next week.