Robbers sprayed a customer in the face with an unknown substance during a raid at a Yorkshire Building Society branch in Wyke.
Two hooded men entered the Towngate store, threatened staff and demanded cash at around 10.30am on Saturday.
Workers activated the security system and the men fled empty handed.
The man who was sprayed by one of the culprits had to be treated in hospital, but was released the same day.
Det Sgt Tim Lofthouse, of Bradford District CID, said: “Clearly this was a very distressing incident for the man who was sprayed and for the staff and other members of the public involved.
“The area would have been very busy at the time and I would appeal for anyone who witnessed the incident to contact us.”
Call Javelin House police station on 01274 474794 or 101. Crimestoppers can also be contacted anonymously on 0800 555 111.