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.