Objective: Porphyromonas gingivalis and Prevotella intermedia are black-pigmented, strictly anaerobic Gram-negative rods and are well known as important periodontopathogens. Although clinical isolates of these species tend to be susceptible to most antimicrobial agents, relatively little information is available on its in vitro antibiotic susceptibility. The purpose of this study was to investigate the presence of P. gingivalis and P. intermedia in patients with chronic periodontitis and gingivitis and to determine the antimicrobial susceptibility to these species to metronidazole and tetracycline. Methods: Bacterial isolation for P. gingivalis and P. intermedia was performed in 94 chronic periodontitis patients and 21 gingivitis patients who attended clinics at the Pontificia Universidad Javeriana. Bacterial sampling was done with paper points in the gingival sulcus, transport took place in thioglycolate broth, and primary culturing was carried out on Wilkins -Chalgren agar in anaerobic conditions. The isolates were identified according to RapID- ANA II system and the antimicrobial susceptibility was determined by using the MIC Evaluator test. Results: In the 94 patients with chronic periodontitis were identified 74 isolates of P. gingivalis and Prevotella species (P. gingivalis n=33, P. asacharolytica n= 1, P. intermedia n=6, P. corporis n= 24, P. melaninogenica n=8, P. disiens n = 2). In the 21 patients with gingivitis only Prevotella species were identified (P. intermedia n=10, P. corporis n=3, P. melaninogenica n=3, P. disiens n=1 and P. horyzihabitans n=1). The 92 isolates were susceptible to metronidazole and only 3 isolates of P. gingivalis and 1 isolate of P. intermedia were resistant to tetracycline with values of 8 ug / ml. Conclusion: P. gingivalis and Prevotella species were found in a high frequency (78.7%) in patients with chronic periodontitis and isolates were highly sensitive to metronidazole and tetracycline. This work was funded in part by Colciencias (Proyect 1203-493-26230).