A pool of blood found near a bridge in Cheshire is human, police have said.
A section of car park near Twinnies Bridge, Wilmslow, was cordoned off for forensic examinations after police made the discovery in the early hours.
Searches of the area and checks with hospitals have failed to find anyone suffering significant blood loss.
Further tests will now be carried out to DNA profile the blood, but police say they do not know if an accident or "something sinister" has taken place.
Cheshire Police have been using sniffer dogs and the force helicopter to search the area around the area of Pownall Park.
Police discovered the blood at 0100 BST and are trying to establish how long it had been there.
They want to hear from anyone who may have information on the cause of its appearance.
"Until further information is known, police cannot determine whether the blood found is as a result of an accident or something more sinister," said a spokeswoman.