Fifty six populations of the potato cyst nematode collected from Northern Bolivia to Southern Colombia were tested on the European host differentials as well as on six additional clones derived from Solanum vernei and S. spegazzinii in order to determine their potential as differentials for the Andean nematode populations. Although S. vernei (VTn)2 62.33.3 was an inefficient host for 32 populations, all differential plants were efficient hosts for most Andean potato cyst nematode populations; thus the expression of variability was limited when British and Dutch differential plants were used. Since there are different systems for classifying races, none of which fitted our findings, a new scheme was developed. Under this scheme British and Dutch races as well as Andean populations of the potato cyst nematode can be identified. © 1977, Brill. All rights reserved.