The fluid challenge is used in the fluid management of many sick patients. The principle behind the fluid challenge technique is that by giving a small amount of fluid in a short period of time, the clinician can assess whether the patient has a preload reserve that can be used to increase the stroke volume with further fluids. The key components of a fluid challenge are described.Dynamic predictors of fluid responsiveness are increasingly used in preference to the central venous and pulmonary artery occlusion pressure. The gold standard to monitor the response to a fluid challenge is using a continuous cardiac output monitoring. Fluid therapy guided by flow monitoring has been shown to reduce hospital stay and postoperative complications.A fluid challenge identifies and simultaneously treats volume depletion, whilst avoiding deleterious consequences of fluid overload through its small volume and targeted administration.