We have reexamined 68 (92%) of 74 donors accepted at this center nine to 15 years ago. There was a moderate but significant increase in BP, and ten donors (15%) were hypertensive at the follow-up. Twenty-six donors (38%) had albumin excretion over 10 micrograms/min or excretion of total protein over 185 mg/24 hr. In four of 16 with increased excretion of total protein, this exceeded 400 mg/24 hr, and in three donors this could be due to an intercurrent disease. Ccr averaged 78.4% of preoperative values, and was less than 50% (range 32 to 49%) in eight donors. The compensatory increase (median 30.5 mliter/min/1.73m2) was inversely correlated with age and BP. Aspects of tubular function were assessed by the diluting capacity during water diuresis and by urinary excretion of beta 2-microglobulin and N-acetyl-beta-glucosaminidase. No consistent abnormalities were observed. A subgroup of donors (N = 32) was compared with a matched control group. Urinary albumin excretion among the donors was significantly higher compared to the controls, both in absolute terms (5.4 vs. 3.3 micrograms/min, P less than 0.002) and as percent of total protein excretion (7.6 vs. 5.7%, P less than 0.05). Otherwise no consistent differences were observed. The development of BP over time warrants further observations, but there is no evidence that uninephrectomy represents a long-term risk to the donors' health.