The role of serum lysozyme in the presence of intra-abdominal sepsis was studied to act as an adjunct to various other modalities used for diagnosing intra-abdominal abscesses. Lysozyme (muramidase) is a bacteriolytic enzyme located within phagocytic cells including leukocytes. We measured serum concentrations of lysozyme by a standard turbidimetric method on three groups of murine models. One group underwent caecal ligation and puncture (CLP), the second group underwent a sham operation, and the third group was used as controls. In mice with intra-abdominal abscesses secondary to caecal ligation and perforation (n 030), the serum lysozyme levels were increased compared to the sham-operated mice (n 030) and controls (n030) (p 0<0.001). In this study, serum lysozyme levels have a high sensitivity and specificity related to the presence of an intra-abdominal abscess in mice. Clinical studies are required to demonstrate its role in humans.