We have examined quantitatively stabilities of PNA/DNA hybrid duplexes with identical nearest-neighbor base pairs and compared stabilities between PNA/DNA and DNA/DNA. The average difference of stabilization energy of the short PNA/DNA was 0.9 kcal mol(-1), which suggests that the stability of the hybrids with identical nearest-neighbor base pairs can be predicted with the nearest-neighbor model as well as those of nucleic acid duplexes.