Introduction. Catheter-associated infection is caused by microorganism colonization of the surface of the implanted catheter with a biofilm formation that significantly increases their resistance to antiseptics and antibiotics, especially in immunosuppression. Low-molecular antibacterial peptides are compounds capable of combating biofilm formation. The aim of the study was to describe morphological characteristics of a catheter-associated infection model on laboratory mice secondary to immunosuppression and to assess the efficacy of the low-molecular cationic antibacterial peptide (warnerin). Materials and methods. An experiment included white outbred mice (25–30 g body weight) under ether anesthesia that received 1.0-cm fragments of intravascular catheters under the skin of the backs. The animals underwent preliminary immunosuppression with cyclophosphamide. We used Staphylococcus epidermidis 33 (in the form of suspensions or biofilms previously grown on catheter segments) and low-molecular cationic peptide warnerin. All animals were sacrificed by ether overdose on days 1, 2, and 3 after the manipulation. We took the tissues surrounding the catheter for histological and immunohistochemical studies with antibodies to CD34, vimentin, CD68, CD3, and CD20. Results. The warnerin administration at the site of the catheter implantation led to disappearance of or a significant decrease in the number of bacterial. In the infiltrate, the number of neutrophils significantly increased, whereas that of fibroblasts decreased. Immunohistochemistry confirmed the features of the cellular reactions around the catheters with bacterial contamination with warnerin administration. Conclusion. In a model of catheter-associated infection in immunosuppressed mice, the warnerin antibacterial manifests in characteristic histological alterations in the inflammatory infiltrate composition. Keywords: catheter-associated infection model, morphology of inflammation, warnerin antibacterial cationic peptide