Former Bosnian Serb general Ratko Mladic is expected to stay in hospital for a second day of tests after being taken ill during his war crimes trial on Thursday, his lawyer said.
Mladic, 70, is accused of genocide over the siege of the Bosnian capital Sarajevo and the 1995 killing of 8,000 Muslim men and boys in Srebrenica, Europe's worst massacre since World War Two.
He was rushed to hospital on Thursday morning after he was taken ill in court. He asked the judge for a break, and then slumped with his head in his hands early on the fourth day of his war crimes trial at the International Criminal Tribunal for the former Yugoslavia (ICTY), based in The Hague.
Already in poor health when arrested in Serbia last year after 16 years on the run, Mladic has several times said he is too ill to stand trial. He complains that he suffers from the effects of a stroke, has problems with his teeth and has been admitted to hospital with pneumonia.
Prosecutors and relatives of victims fear he could die without facing justice, as did former Yugoslav strongman Slobodan Milosevic, who died in a Dutch prison cell in 2006 while on trial before the ICTY.
Tribunal spokeswoman Nerma Jelacic told Reuters: "He (Mladic) complained he was feeling unwell during the hearing, so the hearing was adjourned."
Branko Lukic, Mladic's lawyer, told Reuters the trial was unlikely to continue on Friday.
"He really looked unwell," Lukic told Reuters. "It was a huge surprise for all of us because he'd been looking in pretty good shape."
Lukic said later Mladic's condition had improved, but he would stay in hospital for further tests on Friday.
"He's better than he was this morning, when he couldn't recognize people around him or move his right arm and leg," Lukic said.
A Reuters witness said Mladic asked for a break shortly after Thursday's session opened. He then put his head in his hands, and the judge called for medical staff and adjourned the hearing.
A member of Mladic's defense team had accompanied him to hospital, Lukic said.
Earlier this year, the opening of the trial had to be postponed after it emerged the prosecution had failed to disclose thousands of pages of evidence to the defense.