We describe two patients receiving peritoneal dialysis who experienced refractory peritonitis caused each by Gram-negative bacteria: Acinetobacter baumannii and Stenotrophomonas maltophilia. These patients did not respond to appropriate intraperitoneal antibiotic therapy. We assumed bacterial colonization in the intra-abdominal portion of the catheter with biofilm. Therefore, patients were treated with additional instillation of a ceftazidime-heparin lock into the catheter lumen after each exchange, as an adjunct to systemic antibiotic treatment which was successful. This study suggests that antibiotic lock therapy in the treatment of refractory peritonitis can be an effective method without catheter removal.