Objective: To assess whether the passive leg raising (PLR) test could predict fluid responsiveness and to describe its practical aspects. Summary of findings: Raising the legs to 45° transfers blood from the lower part of the body toward the cardiac chambers, increasing the right and left cardiac preload by a significant extent. The PLR test has been recently developed as a transient and reversible endogenous fluid challenge. An increasing number of studies have tested the ability of PLR for predicting the haemodynamic response to fluid in critically ill patients with acute circulatory failure. These studies established that the PLR effects on descending aortic blood flow, on subaortic blood flow or on pulse contour-derived cardiac output allow predicting fluid responsiveness with very good sensitivity and specificity. All the studies are concordant and the cut-off values of the PLR-induced increase in cardiac output or surrogates are quite similar between studies. It is important that prediction remains fully evaluable in patients with cardiac arrhythmias or spontaneous breathing activity. The PLR test is more accurate when it is started from the semi-recumbent rather than the supine position. Its assessment requires a real-time assessment of cardiac output, as enabled by oesophageal Doppler, echocardiography or pulse contour analysis. Conclusions: PLR is now well demonstrated to be a reliable test for predicting fluid responsiveness, even in patients with spontaneous breathing activity or arrhythmias. © 2010, Nederlandse Vereniging voor Intensive Care.