The relationship between 22 potato species (Solanum spp.) and a range of other solanaceous species (S. melongena, S. dulcamara, Lycopersicon esculentum, Capsicum annuum, Nicotiana tabacum was examined using dot blot hybridization of two probes (pSB1 and pSB7) isolated from Solanum brevidens CPC 2451. Under the most stringent washing conditions, the probes hybridized exclusively with the species from the series Etuberosa (S. brevidens, S. etuberosum and S. fernandezianum). Under less stringent washing conditions hybridization to a larger number of species was observed with both probes. pSB7, but not pSB1, gave a signal in L. esculentum under the least stringent conditions, whereas neither probe hybridized with C. annuum, S. melongena nor N. tabacum. An unweighted logistic regression model was used for estimating the order and distance of each species from S. brevidens CPC 2451. With pSB1, all species differed from S. brevidens CPC 2451 (P = 0.0000–0.0035), and the Etuberosa group differed from the tuber-bearing species (P < 0.0001). The order of species was similar with pSB1 and pSB7, but the P values were not significant with pSB7, indicating less specificity of pSB7 to S. brevidens CPC 2451.