For the assessment of chromosomal numeral aberrations in cells, the method of choice is fluorescent in situ hybridisation (FISH) or, a newly introduced technique, oligonucleotide primed in situ hybridisation (PRINS). In the PRINS method labeled nucleotides are incorporated into newly synthesized DNA mediated through the Taq polymerase. Both PRINS and FISH reactions are visualized with a fluorescent light detection system. We present a method whereby PRINS products can be reliably and rapidly visualized by a streptavidin DAB detection system.