Abstract 1. 1. Effects of sodium loading and dehydration on ANP gene expression were investigated in rats. 2. 2. ANP-mRNA was determined using Northern blot and dot blot hybridization technique with α- 32P-labeled r-preproANP-cDNA probe. Salt loading increased the ANP-mRNA content in atria. Correlation with ANP-mRNA content and the plasma sodium concentration was established. 3. 3. Deprivation of water for 2 and 4 days increased ANP-mRNA 2.1- and 1.6-fold, respectively. 4. 4. These results demonstrated that water-salt balance affects the ANP-gene expression.