A man was pepper-sprayed in the face during a robbery in Croxley Green on Sunday.
Hertfordshire Constabulary is appealing for information after two men in their 20s were approached at about 11.30pm in Watford Road.
Two men, who police are describing as being of Asian appearance, threatened the victims and sprayed one of them in the face before stealing a bag.
Police would like to speak with anyone who was in the area at the time and saw anything suspicious, or saw one of the victims attempt to flag down passing traffic.
Anyone with information can contact DC Adam Bridges on 101 quoting crime reference number C2/14/902 or call Crimestoppers anonymously on 0800 555 111.