The PRimed IN Situ labeling (PRINS) technique is an alternative to in situ hybridization for rapid chromosome screening. We have defined and tested new specific oligonucleotide primers for alpha-satellite DNA of several chromosomes. When using a semiautomatic PRINS protocol, specific labeling was obtained in both metaphase cells and interphase nuclei in a 1-h reaction. PRINS may be a simple and reliable technique for rapidly detecting aneuploidies.