Atrial natriuretic peptide (ANP) is involved in the pathogenesis of sodium-sensitive hypertension. The loss of Sca I restriction site in the ANP precursor gene abolishes the regular stop codon. The aim of our study was the analysis of the Sca I gene polymorphism in 23 patients with sodium-sensitive hypertension, the molecular characteristic of the mutation and the comparison of the blood pressure values, plasma renin activity, plasma ANP and aldosterone concentration between patients with or without mutation. Applying the polymerase chain reaction (PCR), followed by digestion with Sca I, the heterozygous mutation has been found in 9 (39%) patients. The sequencing of PCR products indicated that the loss of Sca I restriction site is caused by T2238-->C transition leading to the translation of ANP with two additional arginines. The higher concentration of ANP in plasma has been found in T2238-->C transition patients on normal and high sodium diet as compared with patients without mutation. These preliminary results suggest that the heterogeneity of sodium-sensitive hypertension is associated with the T2238-->C mutation of the ANP precursor gene.