The primed in situ (PRINS) labelling method was developed as an alternative to classical cytogenetics and fluorescence in situ hybridization (FISH) for the characterization of interspecific somatic hybrids. Full karyotypes were performed by PRINS using Alu-specific primers to generate the painting of all human material associated with R-like banding. The representativity of individual human chromosomes was established using primers specific for discriminent alpha-satellite DNA sequences providing specific signals on the centromeres of the targeted chromosomes and corresponding spots in interphase nuclei. Using this methodology, a somatic hybrid clone was shown to be monochromosomal for the der(11) from a t(11;22) patient.