A man was injured after an attacker sprayed him in the face with what is believed to be ammonia - the latest in a string of similar attacks.
The 20-year-old was allegedly attacked while walking through Lazarus Court - an area packed with bars and restaurants in Doncaster town centre - at about 2.15am on Sunday.
South Yorkshire Police said the substance is believed to be ammonia - a corrosive substance that can cause burns and skin irritation - but samples have been sent away for testing and detectives are awaiting the results.
He was also stabbed during the incident and taken to hospital to be treated for stab wounds to his back and injuries to his face.
This is the latest in a series of similar recent attacks across the country, including one in Sheffield, in which people have been injured after having a substance thrown at them.
A South Yorkshire Police spokesperson said "It was reported a man walking on Lazarus Court, Bradford Row, Doncaster, was sprayed in the face with a substance and assaulted.
"At this time it is not clear what the substance is."
But she added that the substance is "believed to be ammonia, however officers are waiting for this to be confirmed."
This follows a similar incident in Sheffield last week when a woman was hurt after yobs drove past and threw what is believed to be a noxious substance in her face.
The 39-year-old victim was walking along Barnsley Road in Fir Vale when a silver car with three men inside pulled up and one of them hurled a liquid at her that police believe may have contained harmful agents.
The woman was not seriously injured in the attack, which happened on Thursday evening at 7.10pm.
Police have not yet said whether there is a link between the incidents.
These incidents follow a wave of unrelated acid attacks in London in recent months. Five people were attacked with acid thrown in their faces in one night in the capital in July.
Home Secretary Amber Rudd and Met Police boss Cresside Dick yesterday vowed to up “vital” police stop and search powers to clamp down on acid attacks and stabbings.
Ms Rudd said her “purpose is simple: to take as many offensive weapons, knives, guns, acid and harmful drugs out of the pockets of criminals as possible.”
Contact police with information on 101.