A man was flown to hospital by air ambulance after his motorcycle collided with a car.
The incident happened on the A259 Marsh Road between Little Common and Pevensey shortly after 3pm yesterday (Monday).
A 44-year-old man riding a black Harley Davidson Night Rod motorbike and his 55-year-old pillion passenger, both from Eastbourne, each suffered serious injuries.
The driver was flown to St George's Hospital in London by the Kent, Surrey and Sussex Air Ambulance for treatment.
His passenger was taken by land ambulance to the Royal Sussex County Hospital in Brighton.
The 73-year-old driver of the car, a brown Vauxhall Meriva, was unhurt.
The A259 was closed to traffic between Little Common and Pevensey while emergency services dealt with the incident. It did not fully reopen until 6.40 pm.
Anyone who saw what happened and who has not yet spoken to officers is asked to call Sussex Police on 101 or email firstname.lastname@example.org, quoting Operation Kinsham.