The primed in-situ labelling (PRINS) method is an alternative to in-situ hybridization for chromosomal detection based on the use of chromosome-specific oligonucleotide primers. Using this process, we have developed a simple and semi-automatic method for rapid in-situ detection of human chromosomes. The reaction was performed on a programmable temperature cycler. Specific labelling was obtained in < 2 h reaction. Double PRINS techniques were performed on six morphologically abnormal preimplantation embryos using primers specific for chromosomes 9, 16, 18, 21, X and Y. The majority of these embryos displayed chromosomal abnormalities. The present results demonstrate that PRINS may be a simple and reliable technique applicable in human preimplantation diagnosis.