In situ hybridization methods allow the detection of specific DNA sequences on whole chromosomes. The technique has been widely used as a diagnostic and research tool by animal cytogeneticists, for whom detection of unique sequences on mammalian chromosomes is routinely achieved. However, detection of unique sequences on plant chromosomes is less reliable. The recently developed primer-induced in situ hybridization (PRINS) technique allows rapid and reliable in situ detection by the hybridization of primers to denatured target DNA, followed by extension with DNA polymerase in the presence of a labeled nucleotide. The use of short oligonucleotide primers could allow improved penetration of debris and highly condensed chromatin common in preparations of plant chromosomes, thus increasing the sensitivity of in situ detection. The feasibility of this approach is demonstrated by the oligonucleotide primer-mediated detection of the B-hordein gene cluster on a barley chromosome. Applications of the PRINS technique for plant cytogeneticists are discussed.