The presence of functional receptors for human atrial natriuretic hormone in human pheochromocytomas was recently reported. The present study reports the binding of hANH as measured by Scatchard analysis in 4 human adrenal glands and in 5 human pheochromocytomas. Binding assays using [3H]ANH revealed a single class of high-affinity binding sites for hANH in both tissues. Human pheochromocytomas present a lower number of binding sites than normal human adrenal gland (Bmax of 7.1 +/- 2.1 vs 33.6 +/- 6.9 fmol/mg protein, respectively). However, the decreased number of ANH receptors was not paralleled by modifications of tissular cyclic GMP (cGMP). Moreover, plasma hANH concentrations in 7 patients with pheochromocytomas (20.2 +/- 2.7 pmol/l) were statistically higher than those obtained in 25 normal control humans (8.1 +/- 0.6 pmol/l, p less than 0.001). We also demonstrated the presence of immunoreactive ANH in the tumour itself.