A 64-year-old cyclist collapsed and died by the side of the B6268 – the Bedale to Masham road – on Saturday, June 8 at 3.15pm.
The man, from Gateshead, was treated at the scene, near Thornton Watlass, by paramedics but died a short time later.
A spokesman for North Yorkshire Police (NYP) said although the cause of death is not yet known, it is believed to be from natural causes and that no-one else was involved in the incident.
The spokeman added the police are not yet in a position to identify the man, but are now appealing for witnesses.
The cyclist was wearing a Cannondale Liquigas replica cycle jersey, blue shorts, a blue and white helmet and white shoes. He was riding a light coloured racing bike.
Traffic Sergeant John Lumbard, of NYP’s roads policing group, said: “If you saw a cyclist matching the description of the man who died, heading from Bedale to Masham, I ask you to contact the police straight away, as I need to understand his movements prior to a member of the public calling the ambulance service.”
Anyone who can help the police can call 101, select option 2 and ask for Lee Hauxwell. Alternatively information can be emailed to firstname.lastname@example.org.
Please quote reference number 12130092904.