During the summer of 1947, the potato inspectors (Dominion Division of Plant Protection) working in New Brunswick and Nova Scotia were given a course in potato aphid identification based on the methods presented herewith. In nearly all cases a high degree of accuracy was achieved in a few hours of practice. The purpose of this course was to aid the inspectors in determining the potential number of leaf roll vectors present. This paper is given with the hope that the method may be of value to others similarly interested.