Loss of nocturnal decline of blood pressure in hypertension due to chronic renal failure. The aim of this study was to assess the blood pressure profile of chronic renal failure in comparison with essential hypertension. Thirty hypertensive patients with chronic renal failure due to non-vascular nephropathies were matched by age, sex, and mean 24 h blood pressure, with 30 patients affected by uncomplicated mild-to-moderate essential hypertension. They were studied in an open hospital ward. Diet, meal times, sleep times, and activity schedules were standardized. Noninvasive, automatic, blood pressure recordings were performed for 48 h at sampling intervals of 15 min. The mean 24 h blood pressure almost coincided in the two groups. However, in essential hypertension a mean (+/- SD) nocturnal fall of systolic and diastolic blood pressure was found (12.7 +/- 3.8 and 12.9 +/- 4.8 mm Hg, respectively), while renal patients displayed an average nocturnal increase of 2.7 +/- 8.9 mm Hg and 3.7 +/- 7.8 (P less than .001). The renal patients had also higher heart rates, with a significantly blunted nocturnal fall (4.4 +/- 4.5 beats/min as compared to 9.3 +/- 3.1 beats/min of essential hypertension; P less than .001). Among the renal patients, the day-night blood pressure changes showed no significant correlation with age, creatinine clearance, hematocrit, nocturnal change in heart rate, or day or night mean blood pressure levels. These data suggest that an abnormal day-night pattern of blood pressure is present in chronic renal failure patients independently from external interfering factors. Hence, casual measurements of blood pressure confined to daytime may underestimate a hypertensive condition associated with chronic renal failure. 