Saudi Arabia's King Abdullah is suffering from a lung infection and has been breathing through a tube, the country's Royal Court said.
The ailing monarch, who is 90 years old, was admitted to hospital on Wednesday for medical checks.
Abdullah has suffered increasingly frequent health scares in recent years, prompting focus on the line of succession in the oil-rich Gulf state.
He was transferred to a top hospital in the capital of Riyadh on Wednesday after suffering from breathing difficulties.
"After the necessary medical tests by the medical team, it became apparent that there was a lung infection that required the insertion of a tube to aid with breathing on a temporary basis this evening," the Royal Court said in a statement on Friday, as cited by the Saudi state news agency SPA.
The procedure had led to "stability and success", the statement said.
Abdullah assumed the Saudi throne in 2005, following the death of his half-brother King Fahd.
The kingdom remains the world's top oil producer and is home to the holiest sites in Islam.