Two men were taken to hospital following a three-vehicle crash near Helmsdale.
Emergency services, including three fire crews, were called to the scene south of Portgower at around 7.45am on Wednesday.
A section of the A9 Inverness to Thurso road was closed for more than six hours while an investigation was carried out by officers.
The road reopened just after 2pm.
The incident involved a red Renault Megane car, a white Mercedes Sprinter van and a white Vauxhall Vivaro van.
The 36-year-old male driver of the car suffered serious but not life-threatening injuries in the crash.
He was airlifted to Aberdeen Royal Infirmary for treatment.
The 32-year-old male passenger from one of the vans was taken to Raigmore Hospital for treatment to serious injuries, but has since been discharged.
The other three people involved were uninjured.
Police are now appealing to the public for information to establish the full circumstances of the crash.
Sergeant Ally Mackay, from Highlands and Islands road policing unit, said: “Our inquiries into this incident are ongoing and I would urge anyone with information to come forward.
“We would be particularly keen to speak to anyone who saw the vehicles on the road prior to the crash or who may have dashcam footage.
“Anyone with information can call 101, quoting incident 0466 of September 21.”