Tractors worth up to £100,000 each are being stolen to export abroad, Cambridgeshire police have said.
Since the beginning of 2010 there have been at least nine thefts of tractors from farms across the county.
Earlier this month two tractors stolen from a farm in Lincolnshire were recovered in Warboys near Huntingdon.
Pc Simon Page said: "These items of equipment can range in value up to £100,000 and it's thought that they are being sold on elsewhere in Europe."
He said the items stolen were often loaded on to a container or lorry and sold quickly overseas, leaving farmers with a complete loss of revenue as they are unable to maintain their land without them.
"Although there has not been a huge number of tractors stolen it still amounts to a huge loss of property and income to the victims," Mr Page added.
People are being urged to be on the look-out for tractors and other pieces of farm machinery being stored at unusual locations or out on the roads in the middle of the night.