In the present study, oligonucleotide probes based on 16S rRNA were taken to investigate the diversity of oral spirochetes without culture method. This is the first study that revealed oral spirochetes of both presently cultivable and uncultured oral spirochetes in Korean adult periodontitis patients. Subgingival plaque samples were taken from diseased sites(probing depth ${\geq}6\;mm$, experimental group, n=116) and healthy sites(probing depth${\leq}3mm$, control 1 group, n=28) in 29 patients with adult periodontitis, and from 20 periodontally healthy subjects(probing depth${\leq}3mm$, control 2 group, n=100). Following being examined under phase-contrast microscope, all samples were submitted to dot-blot hybridization after polymerase chain reacton with eubacterial primers. 5 species-specific probes(TVIN, TDEN, TMAL, TSOC, and TPEC) and 7 group-specific probes(TRE I, TRE II, TRE III, TRE IV, TRE V, TRE VI, and TRE VII) were used one by one for the identification of both cultivable and so far uncultivable oral spirochetes. All probes were labeled with digoxigenin(DIG)-ddUTP and detected by chemilumininescence. The following results were obtained. 1. Under phase-contrast microscope, 91.37% and 14.28% of oral spirochetes were observed in the experimental and control 1 groups, respectively. None of oral spirochetes were observed in control 2 group. 2. With universal probe, 98.27%, 46.42%, and 22.0% of oral spirochetes were observed in experimental, control 1, and control 2 groups, respectively. 3. With specific probe, 95.68%, 35.71%, and 19.0% of oral spirochetes were observed in experimental, control 1, and control 2 groups, respectively. 4. With species-specific probes, T. socranskii were recovered in a high percentage of sites(81.89%) examined, followed by T. maltophilum(50.0%), T. vincentii(36.20%), T. denticola(13.79%), respectively. With group- specific probes, TRE IV was recovered in a high percentage of sites(85.34%) examined, followed by TRE II(77.58%), TRE I(56.89%), TRE III(25.86%), TRE VI(5.17%), and TRE V(2.58%), respectively. 5. T. vincentii were only observed in the diseased sites, not in the healthy sites. 6. Neither T. pectinovorum nor group VII oral spirochetes were observed in any sites. The findings warrant further investgations of the recovered spirochetes to elucidate the possible associations of oral spirochetal prevalence in race and types of periodontitis, pathogenesis of T. vincentii and the possible distributional change of oral spirochetes before and after treatments.