In senescence renal function is thought to decline markedly even in the absence of renal disease. It has also been proposed that the changes in renal function with age are not uniform and that confounding factors such as hypertension or atherosclerosis may play a role. We performed a comprehensive study to compare several aspects of renal function in four groups: (i) young healthy normotensive subjects (N = 24; 13 males; mean age 26 +/- 3 years); (ii) elderly healthy normotensive subjects (elderly NT; N = 29; 13 males; 68 +/- 7 years); (iii) elderly treated and untreated hypertensive patients (elderly HT; N = 25; 13 males; 70 +/- 6 years); and (iv) elderly patients with compensated mild to moderate heart failure (elderly HF; N = 14; 6 males; 69 +/- 6 years). Compared to young subjects mean GFR (C(In)) and ERPF (C(PAH)) were significantly lower in the elderly, despite similar mean plasma creatinine levels (young, 121 +/- 11, 650 +/- 85 ml/min/1.73 m2; elderly NT, 103 +/- 11, 486 +/- 102; elderly HT, 103 +/- 13, 427 +/- 55; elderly HF, 92 +/- 14, 377 +/- 103). Nevertheless, GFR was within the normal range in the majority of elderly NT and HT, but not in elderly HF. ERPF was significantly lower in elderly HT as compared with elderly NT, and still lower in elderly HF. Mean renovascular resistance and filtration fraction were significantly higher in the elderly, particularly in elderly HT and HF as compared with the young. Mean fractional excretion of Na+ was similar in all groups studied, but the lithium clearance was significantly lower in the elderly, suggesting a greater proximal and less distal sodium reabsorption in senescence. In the elderly, mean PTH concentration and urinary excretion of pyridoline cross-links were significantly higher and mean 25-(OH)D3, calcitriol and phosphate concentrations significantly lower; the correlation between PTH and GFR was significant (r = -0.432, P < 0.001). The results document that the decrease in renal hemodynamics with senescence is less marked than suggested by some studies using less stringent methodology and inclusion criteria. Comorbid conditions confound renal function in the elderly. Age-associated changes in renal hemodynamics are accompanied by significant alterations of renal hormones and of renal sodium handling.