Resistance to the potato cyst nematode (PCN) species Globodera pallida, derived from the wild diploid potato species Solanum vernei, has been investigated. This source of resistance, which is effective against all of the major pathotypes of G. pallida and Globodera rostochiensis, has been assumed to be due to several genetic factors, but it has proved difficult to deploy effectively in breeding strategies for potato cultivars. Diploid and tetraploid potato populations segregating for 'vernei' resistance were analysed. At the tetraploid level, a bulk segregant analysis (BSA) approach was employed and detected AFLP markers linked to a resistance QTL on potato linkage group V. Conventional linkage analysis of a diploid population identified QTL on linkage groups V and IX. A marker linked to a QTL on linkage group V has been converted to a single-locus PCR-based marker, which can be used to detect the presence of the QTL in diploid and tetraploid potato germplasm. Moreover, there is evidence that one of the AFLPs detected by BSA appears to be specific to an introgressed segment of DNA from S. vernei. These results are compared with those obtained from other studies on resistance to the PCN species G. pallida.