The aim of this study was to identify microorganisms from root canals with periapical abscesses and to ascertain the susceptibility of Peptostreptococcus prevotii and Fusobacterium necrophorum to antimicrobials. Study design Thirty root canals were microbiologically sampled by using sterile paper points. The concomitant microorganisms were identified through the use of established methods. The susceptibility of P prevotii and F necrophorum to antimicrobials was evaluated by using the E test method. A total of 117 different bacterial strains were recovered, including 75 strict anaerobes or microphilic species. The most frequently isolated strict anaerobes were P prevotii, Peptostreptococcus micros, and F necrophorum. Facultative bacteria such as Gemella morbillorum and Streptococcus mitis were also found, albeit less frequently. The data revealed that P prevotii and F necrophorum were susceptible to the tested antibiotics. Gram-positive anaerobic bacteria predominate in the mixed microbiota of root canals with periapical abscesses. Moreover, P prevotii and F necrophorum are susceptible to the tested antibiotics.96332-9