Rat adrenal zona glomerulosa cells lost their ability to produce aldosterone from either endogenous precursors or added deoxycorticosterone within 2 days of primary monolayer culture in a medium with a potassium concentration of 6.3 mmol/l. The lost corticosterone methyl oxidase I and II activities were totally regenerated when the ambient potassium concentrations was raised to 31 mmol/l. The conversions of deoxycorticosterone to 18-hydroxycorticosterone and aldosterone were completely restored by culture in a high-potassium medium also in zona glomerulosa cells of rats in which aldosterone biosynthesis had been suppressed by potassium restriction and sodium loading. However, these conversions were not induced in zona fasciculata-reticularis cells. The induction of aldosterone biosynthesis was associated with the appearance of a mitochondrial 49,000 protein cross-reacting with an antibody raised against bovine adrenal cytochrome P-450(11) beta. Thus primary cultures of zona glomerulosa cells are promising models for studying in vitro the molecular mechanisms of long-term adaptation of aldosterone biosynthesis to sodium and potassium intake.