A fluorescence in situ hybridization (FISH) technique was used for elucidating the telomeric sequence and its chromosomal location in the Pacific abalone Haliotis discus hannai. The vertebrate telomere PNA (peptide nucleic acid) probe, the oligonucleotide (TTAGGG)₇ and (TTAGG)₇ probes were used for the analysis. FISH with the PNA and (TTAGGG)₇ oligonucleotide probes displayed clearly defined signals on the telomeric regions of all metaphase chromosomes and interphase nuclei. On the other hand, the (TTAGG)₇ probe, which has one base less than probe (TTAGGG)₇, did not display clearly defined signals. These results suggest that the telomere of H. d. hannai is composed of a (TTAGGG)_n sequence, which is typically found in vertebrates and other molluscs. FISH-derived signals were not observed at interstitial sites of H. d. hannai chromosomes. Hence, this species is unlikely to possess any nontelomeric sites of the telomeric sequence. The successful use of FISH in this study suggests that the FISH technique may also be extended for other analytical purposes pertaining to this and other abalone species.