The aim of this paper was to study the effects of essential fatty acid (EFA) on fractional sodium excretion (FE(Na(+))) and renal hemodynamics in rats during hydropenia (H) and acute volume expansion (VE), successively. Mean arterial pressure (MAP) and renal blood flow (RBF) were measured using a blood pressure transducer and a flow probe, respectively, both connected to a flowmeter. Glomerular filtration rate (GFR) was estimated by inulin clearance. The rats receiving coconut oil as only source of dietary lipids (the EFA-deficient group) presented lower levels of linoleic acid in cortex and medulla and lower body weight than the rats receiving soy oil in place of coconut oil (the control non-EFA-deficient group). During H, the EFA-deficient rats exhibited a lower level of renal vascular resistance resulting in a higher level of RBF and a higher urinary flow (V') and FE(Na(+)), although GFR was lower than in the control group. During VE, the rats of the control group responded with increased MAP, RBF, V' and FE(Na(+)), which were not found in the EFA-deficient group, suggesting an impaired hemodynamic adjustment in EFA deficiency. In conclusion, both experimental conditions revealed that EFA deficiency affects the renal hemodynamics.