To determine if pregnancy alters the impaired renal vasodilator responses in hypertensive Dahl salt-sensitive (Dahl S) rats, we measured glomerular filtration rate and effective renal plasma flow and calculated renal vascular resistance before, during, and after renal vasodilation with glycine (0.17 mmol/kg per minute IV). Conscious, midterm (day 11 to 14) pregnant and age-matched virgin Dahl S and Dahl salt-resistant (Dahl R) rats were fed an 8% NaCl diet for 4 weeks (n=6 per group). Mean arterial pressure was elevated (P<.05) in Dahl S compared with Dahl R rats, with no significant difference between pregnant and virgin animals in either group. Pregnancy resulted in significant increases in plasma volume, baseline glomerular filtration rate, and renal plasma flow and a significant decrease in renal vascular resistance. The glycine-induced increase in filtration rate in virgin Dahl S rats (27±4%) was less (P<.01) than pregnant Dahl S (60±4%) and either group of Dahl R (virgin, 43±3%; pregnant, 45±5%) rats. Similarly, the 21 ±4% increase in renal plasma flow in virgin Dahl S rats was less (P≤.01) than the pregnant Dahl S (45±4%) and either pregnant (45±5%) or virgin (45±5%) Dahl R rats. Glycine decreased renal vascular resistance only 12±2% in the virgin Dahl S compared with 31±3% in the pregnant Dahl S rats and 30±4% and 28±3% in pregnant and virgin Dahl R rats. In summary, the impaired renal vasodilator response in Dahl S rats is restored by pregnancy.