Objectives: To present a case of endodontic failure obturated with a methacrylate-based root filling material, Resilon/ RealSeal (RS). To determine if RS is susceptible to biodegradation by endodontically relevant microbes by a method known to show RS degradation. Method and Materials: Emulsions of RS were dispersed in agar with minimal bacterial nutrients in culture plates. Lipase PS served as a positive control. Pseudomonas aeruginosa, Fusobacterium nucleatum, Prevotella intermedia, Porphyromonas gingivalis, Porphyromonas asaccharolytica, Enterococcus faecalis, Streptococcus sanguis, Streptococcus mutans, Staphylococcus aureus, and Staphylococcus epidermidis were tested for their ability to biodegrade RS. The bacteria were inoculated in the plates and examined daily for RS degradation for 7 days. Results: Degradation of the emulsified RS manifested in the formation of clear zones around P aeruginosa, P intermedia, P asaccharolytica, S aureus, and S epidermidis. No degradation was seen with the other tested bacteria or in plates that did not contain RS emulsion. Conclusion: Endodontic pathogenic bacteria can degrade RS. These findings complement other work and suggest that the seal and integrity of root canal fillings obturated with RS may be impaired by a microbial insult. Keywords: clear zone, degradation, endodontic bacteria, Resilon, root canal treatment failure