Ukrainian opposition leader Viktor Yushchenko has returned to Austria for new tests in connection with a mystery illness he developed three weeks ago.
Yushchenko looked haggard after his first hospital stay
The presidential candidate entered a Vienna clinic with an acute stomach complaint on 10 September but was later released and returned to campaigning.
Doctors have distanced themselves from initial reports that he was poisoned.
His office said he was well, but was returning to the Rudolfinerhaus clinic for new tests lasting several days.
The clinic took the unusual step on Wednesday of issuing a statement to deny having found any evidence of poisoning during the initial examination.
"We are unable to assess the cause [of the illness] so far," Dr Michael Zimpfer, head of the intensive care unit at Rudolfinerhaus, told reporters.
Mr Yushchenko's own doctor, Mykola Korpan, said on the same day that the diagnosis was still open.
"The cause or causes of the condition are still fully open and will require further examination," he said.
Mr Yushchenko is in a close race for the 31 October election with Prime Minister Viktor Yanukovich, who is backed by outgoing President Leonid Kuchma.
His campaign manager, Oleksander Zinchenko, announced on 17 September that said there was "enough evidence" to speak of an "attempt on [Mr Yushchenko's] life".
The candidate had been taken ill after a dinner on 5 September with top Ukrainian security officials, including the head of the Security Service of Ukraine (SBU), Ihor Smeshko.
Mr Smeshko told parliament this week that it was a "matter of honour" for the SBU to investigate the poisoning allegations and he urged the candidate to undergo a forensic examination.
"We will do everything to resolve the case as soon as possible," he told reporters.