At 6 pm on Sunday, police and an ambulance were alerted to Tierp after a man in his 30s was injured in the neck.
When blue light staff arrived, it was discovered that the man had been stabbed in the neck.
The man, who is in his 30s, was taken urgently by ambulance to hospital with what the police describe as "serious injuries".
A man in his 35s and a woman, suspected of attempted murder and aiding and abetting the crime, were arrested in close proximity to the injured man.
Prosecutors later chose to arrest the man while the woman was released.