GISH (genomic in situ hybridization) was applied for the analysis of mitotic chromosome constitutions of somatic hybrids and their derivatives between dihaploid clones of cultivated potato (Solanum tuberosum L.) (2n = 2x = 24, AA genome) and the diploid, non-tuberous, wild species Solanum brevidens Phil. (2n = 2x = 24, EE genome). Of the primary somatic hybrids, both tetraploid (2n = 4x) and hexaploid (2n = 6x) plants were found with the genomic constitutions of AAEE and AAEEEE, respectively. Androgenic haploids (somatohaploids) derived from the tetraploid somatic hybrids had the genomic constitutions of AE (2n = 2x = 24) and haploids originating from the hexaploid hybrids were triploid AEE (2n = 3x = 33 and 2n = 3x = 36). As a result of subsequent somatic hybridization from a fusion between dihaploid S. tuberosum (2n = 2x = 24, genome AA) and a triploid somatohaploid (2n = 3x = 33, genome AEE), second-generation somatic hybrids were obtained. These somatic hybrids were pentaploids (2n = 5x, genome AAAEE), but had variable chromosome numbers. GISH analysis revealed that both primary and second-generation somatic hybrids had lost more chromosomes of S. brevidens than of S. tuberosum.