We localized aldosterone synthase in specific cells in rat and human adrenals. Rat and young (<12 years old) human adrenals have a layered functional zonation. Aldosterone-producing cell clusters (APCCs) replace this zonation in human adults. We recently reported possible APCC-to-APA transitional lesions (pAATLs). We review our CYP11B2 work in this manuscript and add new pAATL cases.