The influence of sodium intake on the gene expression and circulating levels of atrial natriuretic factor (ANF) was investigated in unanesthetized rats with one-kidney, one-clip renal hypertension. After clipping, the rats were maintained for 3 weeks either on a salt-deficient (n = 11) or a regular-sodium diet (n = 10). Animals which had received the regular-sodium diet exhibited significantly higher ANF mRNA levels in their right and left atria than salt-restricted animals, whereas there was no significant difference in plasma ANF levels.