Dietary supplementation with polyunsaturated fatty acids (PUFAs) has been shown to alter the course of experimental renal disease. Although hemodynamic factors such as glomerular hypertension are felt to be important in the progression of renal disease, the effects of dietary PUFA supplementation on glomerular hemodynamics are unknown. The present investigation, therefore, was designed to evaluate the glomerular hemodynamic effects of dietary PUFA supplementation in normal rats. Male Sprague-Dawley rats were fed standard chow supplemented with either 20% (wt/wt) fish oil (FO) as a source of omega-3 PUFAs, 20% sunflower oil (SO) as a source of omega-6 PUFAs, or 20% coconut oil (CO) as a control diet. Micropuncture studies were performed after 4 to 6 weeks of dietary supplementation. Compared with CO rats, SO rats did not demonstrate any changes in glomerular hemodynamics. However, rats supplemented with FO demonstrated significant (p less than 0.05) increases in both single nephron glomerular filtration rate and single nephron plasma flow. These hemodynamic changes were not associated with alterations in glomerular capillary hydraulic pressure or the glomerular ultrafiltration coefficient. The increase in SNPF was primarily the consequence of a 37% reduction (p less than 0.05) in efferent arteriolar resistance. Thus dietary FO supplementation resulted in glomerular hyperfiltration and hyperperfusion. These hemodynamic actions may have important consequences in determining the effect of omega-3 PUFAs on the course of experimental and clinical renal disease.