Police are hunting for sheep rustlers after more than 100 of the animals were stolen from farmland in Bakewell.
Around 105 mule and crop ewes, aged between two and five, were taken between September and this month.
All had flock markings in red on their backs.
Officers are urging members of Farm Watch, a scheme aimed at helping to cut rural crime and protecting Derbyshire’s farming communities which was launched last year, to be extra vigilant.
Sergeant Steve England said: “We have had a number of sheep being stolen over a five-month period and I would like to encourage farmers to ensure that their livestock are marked with the correct equipment and that their land is properly secure.
“I would urge all farmers to remain vigilant and to report any suspicious activity or vehicles to police to help us to prevent a crime before it happens.”
Anyone with information should call the police on 101, quoting crime number 1998/14, or Crimestoppers, anonymously, on 0800 555 111.