This paper considers the suitability of north‐east Yorkshire as a centre for the production of high‐grade seed potatoes, taking the number of aphid vectors of virus diseases as the criterion. Counts of aphids were made during three consecutive seasons on selected fields on the higher land in this area. These counts are related to the various geographical, climatic and biological factors found in each field and conclusions are drawn as to the most suitable districts within the area and the type of field which is likely to prove most satisfactory for this c