Renal expression of neutrophil gelatinase-associated lipocalin (NGAL) increses dramatically after renal ischemia orexposure to nephrotoxic agents. The usefulness of NGAL as a marker of renal injury leading to acute renal failure (ARF) has previously been demonstrated in patient groups that have few confounding factors such as sepsis or cancer. The aim of the present study was to test the usefulness of NGAL levels for predicting a requirement for renal replacement therapy (RRT) in unselected critically ill patients admitted to intensive care.