In twenty-five outpatients with essential hypertension, the relevance of renal kallikrein excretion for inter-individual differences in the blood pressure response to changes in dietary sodium intake was investigated. The patients were studied during 2 weeks of high (300 mmol) and 2 weeks of low (50-100 mmol) sodium intake. In addition there were two control periods of normal sodium intake, one lasting 4 weeks at the beginning and one lasting 2 weeks at the end of the study. Blood pressure, body weight and 24 h urinary sodium and kallikrein excretion were measured at the end of all periods. At the end of the first control period, 1 mg furosemide per kg body weight was administered intravenously, and the urinary excretion of kallikrein and sodium were measured 30 and 120 min later. The difference in mean arterial pressure (delta MAP) between high and low sodium intake ranged from + 18 to -8 mmHg. The eight patients with a delta MAP greater than 10 mmHg were regarded as salt-sensitive. They were older and had a higher initial blood pressure than salt-insensitive patients. For all patients, urinary kallikrein excretion at the end of the low sodium period (123(SEM 20.3) micrograms 24 h-1) was significantly higher than at the end of the first control period (96(SEM 16.3) micrograms 24 h-1, P less than 0.01) and at the end of the high sodium period (96(SEM 23.7) micrograms 24(-1), P less than 0.01). When compared with salt-insensitive patients, salt-sensitives had lower levels of urinary kallikrein excretion and a blunted kallikrein response to dietary sodium restriction and furosemide.(ABSTRACT TRUNCATED AT 250 WORDS)