Police are hunting two men following four suspected acid attacks in less than 90 minutes in east London.
One victim was said to have suffered "life-changing" injuries during one of the attacks late on Thursday.
The Metropolitan Police say the incidents appear to be linked and two involved victims having their mopeds stolen.
The attackers pulled up to the four separate men and doused them in the corrosive liquid, police say.
At the start of the spree, a 32-year-old moped driver had been approached by the pair as he drove in Hackney.
The two male suspects had tossed the noxious substance into his face before one of them jumped on his vehicle and the other drove away on the vehicle on which they arrived.
About 40 minutes later, another victim was attacked in Shoreditch by two men on a moped, having liquid thrown in his face.
Within 15 minutes the attackers appear to have struck again, launching the corrosive substance at a man in Stoke Newington, causing "life-changing" injuries.
The final assault was reported to police at 11.37pm (8.27am on Friday AEST), with a man confronted as he sat on his moped in traffic in Clapton.
After again spraying the liquid in a victim's face, the moped was stolen and both attackers fled.
All four victims were taken to hospital.
"Inquiries are ongoing and officers from Hackney are currently trying to trace the suspects concerned," the Met Police said.