Pseudohypoaldosteronism is thought to be a rare salt-losing disorder, caused by resistance to the action of aldosterone. Defective aldosterone receptor binding is present in familial as well as sporadic cases and it has been suggested that the pathogenesis is due to a defect in the aldosterone receptor system. To date, however, molecular genetic analysis has been unable to identify a mutation in the aldosterone receptor gene itself. We have reviewed the findings in patients with pseudohypoaldosteronism, for clues which might enable us to identify the underlying pathogenesis. Although aldosterone receptor binding is regularly decreased or absent in monocytes of patients with pseudohypoaldosteronism, in some patients receptor protein can be detected with a fluorescence-labeled antibody. Receptor protein was detected in patients from familial autosomal dominant families and in sporadic cases, but was undetectable in two patients with the familial recessive form. To further elucidate the pattern of inheritance we studied the response of the renin-angiotensin-aldosterone system to the stimulation by sodium depletion in the familial autosomal dominant form and in two families with sporadic cases. In both "sporadic" families investigated, one parent and one sibling had an exaggerated response of renin and aldosterone to sodium depletion indicating a defect of sodium conservation apparent only during stress, leading to reclassification as familial cases. No additional family member in the "classical" autosomal dominant families responded abnormally to sodium depletion. These findings indicate that pseudohypoaldosteronism is unusually heterogeneous in its clinical, biochemical, and genetic presentations and findings and suggest that its pathogenesis is heterogeneous as well.