Salt may be involved in the pathogenesis of essential hypertension but no agreement has been reached on how salt might exert its blood pressure control. One reason for the conflicting results could be differences in response to changes in salt intake--i.e. between salt-sensitive and salt-resistant subjects. Hypertension reflects a hemodynamic disturbance: mainly an increase in total peripheral resistance. In order to determine whether central hemodynamics is different in salt-sensitive and salt-resistant essential hypertension, a study was carried out on 37 patients aged 31-63 years with mean casual blood pressure 165/104 mmHg. Based on an increase in ambulatory 24-h mean blood pressure of > or = 10% after one week of dietary salt loading (260 mmol NaCl/24 h) following a one-week salt depletion period (60 mmol NaCl/24 h), 7 patients (19%) were classified as salt sensitive and 30 patients (81%) as salt resistant. Before the salt-sensitivity test, while patients were on their habitual salt intake (160 mmol NaCl/24 h), central hemodynamics (intra-arterial pressure, cardiac output by dye dilution, heart rate by electrocardiogram, and total peripheral resistance) was examined at rest and during bicycle exercise. None of the central hemodynamic variables were different between the two groups, despite a marked difference in blood pressure response to one week of salt loading between the salt-sensitive and the salt-resistant groups (27/9 mmHg vs -2/1 mmHg). Furthermore, no statistically significant differences were observed in neurohumoral variables or echocardiographic indices of left ventricular dimensions between the two groups. Owing to the invasive hemodynamic procedure, central hemodynamics was not restudied during high- or low salt intake. It is concluded that there is no difference in central hemodynamics in salt-sensitive and salt-resistant hypertensive patients when they are on their habitual salt diet.