A bacteriological investigation has been made in two cases of persistent periapical infections. Neither of the two infections responded to root canal therapy including penicillin or penicillin and erythromycin. Samples were taken aseptically for bacteriological examination through the root canals. Chloroform-washed, sterile paper points were used for sampling. Cultivation was performed immediately at chairside on Kanamycin-Vancomycin laked blood agar (KVLB) and blood agar supplemented with menadione, cysteine and glucose for anaerobic incubation and chocolate agar for aerobic incubation.Enterobacter cloacaewas only isolate in case 1;Klebsiella pneumoniaeand enterococci were found in case 2. Obligately anaerobic bacteria were not found. The treatment was successful after antibiotic therapy based on susceptibility testing of the isolates. The route of infection by facultative enteric rods is discussed.