Gravely ill Kremlin critic Alexei Navalny was evacuated to Germany for medical treatment on Saturday (August 22).
He was flown out of the Siberian city of Omsk in an air ambulance - before being taken to a hospital in Berlin.
The long-time opponent of Russia's President Vladimir Putin - and a campaigner against corruption - collapsed on a plane on Thursday (August 20), after drinking tea his allies believe was laced with poison.
If this theory is confirmed - it would be the latest poisoning of someone who has fallen out with the Kremlin, which denies settling scores with its foes by murdering them.
On arrival in Berlin, 44-year-old Navalny was rushed in a convoy of ambulance and police cars to the city's Charite hospital complex.
In a statement, the hospital said it would provide an update on his condition once tests had been completed - adding this could take some time.
Medical staff at the hospital in Omsk said Friday (August 21) evening that he was in an induced coma - and that his life was not in immediate danger.
German doctors had flown there to evacuate Navalny at the request of his wife and allies who said that the hospital treating him was badly equipped.
Navalny has been a large thorn in the Kremlin's side for more than a decade, exposing what he says is high-level graft and mobilizing rallies that draw crowds of young protesters.
Russian medical staff in Siberia had initially said on Friday that while Navalny's condition had improved slightly overnight, he was not well enough to be safely transported out of the country.
They later said they would not object to him being moved - after the German doctors deemed him fit to travel.
Navalny's allies have said they feared authorities in Russia might try to cover up clues as to how he fell ill.