The development of nucleic acid analogues has become an important feature due to the potential use of this new biomolecular tool in genetic diagnostics and investigations. Among all the synthetic oligonucleotides designed, the peptide nucleic acids (PNA) constitute a remarkable class of nucleic acid mimics, with important physico-chemical properties which have been exploited to develop a wide range of powerful biomolecular tools, including molecular probes, biosensors and anti-gene agents. New applications of PNA involve their use as hybridization probes, and consequently the PNA technology is now developing within the field of in situ hybridization techniques. Recent studies have reported the successful use of centromeric PNA probes on human lymphocytes, sperm as well as on isolated oocytes and blastomeres. Muticolour PNA protocols have been described for the specific identification of several human chromosomes. These data show that PNA could become a powerful complement to fluorescence in situ hybridization (FISH) for in situ chromosomal investigation, especially on isolated cells. The present paper gives an overview of the properties of PNA and the assays exploiting PNA technology in molecular genetics and cytogenetics.