Neutrophil gelatinase-associated lipocalin (NGAL) is a 21-kD protein of the lipocalin superfamily. NGAL is a critical component of innate immunity to bacterial infection and is expressed by immune cells, hepatocytes and renal tubular cells in various disease states. NGAL is a small secreted polypeptide that is protease resistant and thus may be easily detected in the urine. Neutrophil gelatinase-associated lipocalin (Ngal, also known as lcn2) was identified as one of the most upregulated genes in the early post-ischaemic mouse kidney, a finding that has now been confirmed in several other transcriptome profiling studies following ischaemic and nephrotoxic kidney injuries. Downstream proteomic studies have also revealed NGAL to be one of the earliest and most robustly induced proteins in the kidney after ischaemic or nephrotoxic AKI in animal models. Importantly, NGAL protein is easily detected in the blood and urine soon after AKI in pre-clinical studies. These findings have initiated a number of translational studies to evaluate NGAL as a novel biomarker in human AKI.