There is evidence to suggest that renal function may alter in the presence of autonomic neuropathy. Albumin excretion rate (AER) and sodium excretion rate (NaER) in timed daytime (erect) and night-time (supine) urine collections were assessed in 20 insulin-treated diabetics with and in 20 without established autonomic neuropathy, matched for age, sex, duration of diabetes, diabetic control, and systolic blood pressure. All patients were free of proteinuria on albustix testing and had normal serum levels of urea and creatinine. AER based on daytime and pooled 24-hour collections was higher, but not significantly so, in the group with autonomic neuropathy. The nocturnal AER on the other hand was significantly elevated in the group with autonomic neuropathy (p less than 0.02) as was the nocturnal urine volume (p less than 0.01) and sodium excretion rate (p less than 0.05). The corrected nocturnal albumin/creatinine ratio was likewise greater in this group (p less than 0.02). These findings suggest that autonomic neuropathy can independently affect renal function and that nocturnal renal haemodynamics and glomerulotubular balance may be deranged in insulin-treated diabetics with autonomic neuropathy.