We studied, under outpatient conditions, nine patients with autosomal dominant polycystic kidney disease who were hypertensive on their usual diet, and nine normotensive healthy probands. The subjects were examined in random order on the 7th day after equilibration on a low-sodium diet (20 mmol/day) and again on the 7th day after equilibration on the same diet but with added sodium to yield a final intake of 200 mmol/day (or vice versa). Blood pressure was monitored non-invasively for 2 h at 4-min intervals using an automatic system. In healthy probands, mean arterial pressure (MAP) was similar on the low- and the high-sodium diets (92.7 versus 91.9 mmHg). In hypertensive patients, a significant (P less than 0.02) increase in mean MAP (107.2 versus 111.2 mmHg) and in systolic blood pressure (140.6 versus 148.7 mmHg) was observed irrespective of whether the glomerular filtration rate (GFR) was normal or reduced. The natriuresis pressure curve showed an upward shift (resetting) and a positive slope (sodium sensitivity). Patients with a reduced GFR as shown by inulin clearance differed from probands and patients with a normal GFR, by showing greater proportional changes in GFR and body weight. In hypertensive patients, atrial natriuretic factor (ANF) levels were higher at baseline and showed an exaggerated response to sodium loading. Changes in angiotensin II (Ang II) or in Ang II binding sites on platelets were similar in patients and controls and changed appropriately with the sodium intake. These data show a resetting of the natriuresis-blood pressure relationship and an increased blood pressure sensitivity to sodium in hypertensive patients with adult, dominant, polycystic kidney disease.