The incident happened at around 2.10pm on Friday when the green BMW R NineT motorbike collided with a white Fiat Fiorino van on the road's junction with the A937, near Laurencekirk.
The 46-year-old male motorcyclist was taken to Aberdeen Royal Infirmary. The 53-year-old male driver of the van was taken to the same hospital with minor injuries and the road was closed for around ten hours.
Sergeant Craig McNeill said: "I would ask if you were driving in the area at the time and may have seen the van or the motorbike prior to the crash that you come forward and speak to officers.
"If there are any motorists with dashcam footage that were in the area around that time, please get in touch with police."
Police can be contacted on 101, quoting incident number 1879 of July 2.