We evaluated the effect of the dihydropyridine Ca-channel blocker nitrendipine on blood pressure (BP) and electrolyte urinary excretion after acute and chronic therapy in 33 patients with different NaCl sensitivity as assessed by a modification of the test of Grim and colleagues. Acute nitrendipine administration significantly reduced BP in the group as a whole, although the hypotensive effect was greater in patients with greater NaCl sensitivity; this difference was still evident after 1 month of chronic therapy. Furthermore, urinary sodium and calcium excretion significantly increased in the 3 h after nitrendipine administration during both acute and chronic therapy: these effects on electrolyte excretion were independent of the NaCl sensitivity of the subject.