We used pre-annealing of differently labelled total genomic DNA probes to perform simultaneous genomic in situ hybridization on mitotic and meiotic chromosomes of interspecific hybrids between plant species of the Tribe Triticeae. The species origin of chromosomes was demonstrated by a two-colour fluorescence after in situ hybridization with directly labelled probes incorporating fluorescein (visualized green) and rhodamine (visualized red). The pre-annealing blocked out common DNA sequences between the different genomes, hence increasing species specificity of the probes. The method is simple and rapid because the hybridization takes only about 2 h, including the pre-annealing step, and hence the whole process can be accomplished easily within a working day making it suitable for routine analysis of chromosomes and genomes.