Neutrophil gelatinase-associated lipocalin (NGAL), a protein involved in iron handling, has been recognized as a marker of inflammation. In this regard, serum and urine NGAL levels have proven a useful diagnostic tool for acute kidney injury. Bacterial peritonitis is an all too common complication of peritoneal dialysis (PD) and while diagnosis in most cases is routine, there are times when patients present with typical symptoms but do not have an elevated PD effluent white blood cell count. Furthermore, patients may present with an elevated PD fluid white count, a cloudy effluent and no evidence of active infection. In these cases, a discriminating role for peritoneal fluid NGAL would be useful to distinguish bacterial and nonbacterial PD fluid infection. A small case control study was performed which demonstrated a very high sensitivity and specificity for peritoneal fluid NGAL. These preliminary data show that peritoneal fluid NGAL may be a useful tool for the early and accurate diagnosis of peritonitis.