Buzz Aldrin, the second man on the Moon, has been evacuated from the South Pole after falling ill.
The 86-year-old former astronaut was visiting Antarctica in a tourist group and was evacuated to New Zealand.
He has fluid in his lungs but is responding well to treatment, a statement on his website said. He is being kept overnight for observation.
Mr Aldrin’s manager Christina Korp, who accompanied him, said he was in good spirits.
She described the last 24 hours as “gruelling”, posting a picture on Twitter of Mr Aldrin giving the thumbs up while being lifted on a stretcher.
Mr Aldrin was flown from a US research centre on the Antarctic coast to the city of Christchurch in New Zealand.
He had tweeted about the tour just a few days earlier.
On Sunday he joked, in a tweet that he might be underdressed for the cold.
Who is Buzz Aldrin?
The former astronaut was part of the Apollo 11 mission which was the first space trip that sent humans to the Moon. During the mission he was accompanied by astronaut Neil Armstrong, who took the first steps on the Moon – Mr Aldrin followed minutes later.
Mr Aldrin has remained in the limelight in recent years, delivering cameo appearances in hit American television shows such as the Big Bang Theory, The Simpsons and 30 Rock.
In 2002, he escaped assault charges after punching a man who demanded he swear on a Bible that the Moon landing was not staged.
In recent years he has called for the colonisation of the planet Mars. In 2015, he spoke to the BBC’s Radio 4, saying: “We’ll lay out preparations up to that [going to Mars], in my mind we are doing it right now.”