Two pairs of sisters with primary aldosteronism are presented. In each pair there was one of the siblings with a unilateral adrenal adenoma and the other with bilateral adrenal hyperplasia. A 4-day dexamethasone trial (2 mg/day) caused a decrease but not a suppression of aldosterone in all patients. Remission of hypertension followed adrenalectomy in the two patients with adenoma. Analysis of DNA in peripheral leukocytes included: 1) the presence of the glucocorticoid-remediable aldosteronism (GRA) chimeric gene originating from crossing over between the 11β-hydroxylase (CYP11B1) and aldosterone synthase (CYP11B2) gene; 2) the occurrence of three polymorphic variants of the CYP11B2 gene possibly causing increased aldosterone synthase activity; 3) mutations in exons 5 and 6 of the CYP11B1 gene leading to conversion of 11β-hydroxylase to an aldosterone-producing enzyme. No GRA chimeric gene, no polymorphic variants of CYP11B2 gene, and no mutations of CYP11B1 gene were detected in the patients. The cause of this familial aldosteronism does not appear to reside in either the CYP11B1 or CYP11B2 gene. The molecular basis of this disorder remains obscure.