1. Plasma immunoreactive human atrial natriuretic peptide (Ir-ANP) levels were measured in eight patients with chronic renal failure who were volume-expanded and during treatment by sequential ultrafiltration and haemodialysis. One patient was studied at two separate treatment sessions.
2. Plasma Ir-ANP levels were raised in all patients (mean ± SE 184 ± 44 pmol/l, n = 9) compared with healthy controls (11 ± 1.4 pmol/l), but showed considerable inter-patient variability.
3. Plasma Ir-ANP levels fell with fluid removal during ultrafiltration (123 ± 30 pmol/l, n = 9, P < 0.02) and again as fluid was removed during haemodialysis (76 ± 20 pmol/l, n = 9, P < 0.02).
4. Seven patients studied 48 h later, before their next dialysis treatment, had regained weight and showed a coincident rise in circulating plasma Ir-ANP (130 ± 33 pmol/l, n = 7).
5. Our data would support the hypothesis that the secretion of ANP is determined by volume or by a stimulus related to volume. However, it does not exclude the possibility that a factor other than extracellular fluid volume expansion contributes to the raised plasma Ir-ANP levels in chronic renal failure.