Thirty-one patients with essential hypertension (81.6 +/- 6.9 years old) were studied during two different regimens of sodium intake: 120 meq/day for 8 weeks and 344 meq/day for 2 weeks. Systemic hemodynamic data were measured with Doppler echocardiography from which the mitral flow velocity integral, cardiac index, and total peripheral resistance were calculated. The salt-sensitive patients in whom the increase in total peripheral resistance was greater than the increase in cardiac index with salt loading were termed SST. In the salt-sensitive patients termed SSC, the increase in cardiac index was greater than the increase in total peripheral resistance with increased sodium intake. All SST patients on day 7 of the high sodium diet remained in the SST group on day 14. Nine of 13 patients in the SSC group on day 7 remained in the SSC group on day 14, and the remaining four patients in the SSC group on day 7 fell into the SST group on day 14. Four of eight non-salt-sensitive (NSS) patients on day 7 of the high salt regimen remained in the NSS group on day 14, whereas the remaining four patients in the NSS group on day 7 fell into the SSC group on day 14. Our data suggest a changing pattern with sodium loading of initially high cardiac index followed by a persistently raised total peripheral resistance. The celiac, superior mesenteric, and renal arteries vasoconstricted with sodium repletion in both SST and SSC patients. With salt loading, the terminal aortic vascular bed vasodilated in the SSC patients and vasoconstricted in the SST patients.