The advent of molecular genetic techniques has brought forth new procedures for in situ chromosomal analysis. One of these techniques is the primed in situ labeling (PRINS) procedure, which constitutes a fast and efficient alternative to conventional fluorescence in situ hybridization for nucleic acid detection. Based on the use of chromosome-specific primers, the PRINS method combines the high sensitivity of the PCR reaction with the cytological localization of DNA sequences. Since its introduction, the PRINS protocol has been optimized, and numerous applications have been developed. The technique has thus proved to be a useful tool for in situ chromosomal screening, and has become a simple and efficient complement to conventional and molecular cytogenetic methods.