Nitrendipine is a dihydropyridine calcium antagonist suggested to be a new drug for first-line antihypertensive therapy, possibly active in once-daily administration. In the present study the acute and long-term hypotensive effects of nitrendipine have been evaluated in comparison with those of atenolol in a randomized, double-blind, clinical trial. Twenty-four patients have been studied, and the effects of treatment have been evaluated both at rest and during psychological and physiological stresses. Hemodynamic noninvasive parameters have also been obtained, at rest and during mental arithmetic tests, by a continuous-wave Doppler technique. Preliminary results about the first 13 consecutive patients are reported here. Nitrendipine induced a highly significant acute hypotensive effect (2 h after drug administration), whereas no effect was observed for atenolol except for heart rate. During chronic treatment (5 weeks), nitrendipine showed less hypotensive effect than atenolol when BP values 24 h after the last administration were analyzed, but significantly more effect when values obtained 2 h after drug administration were evaluated. These findings confirm that nitrendipine is effective in decreasing blood pressure, but the once-daily administration may not bring about the maximum effect in all patients. Interesting aspects of this drug, which make the clinical use of this compound safe, are represented by apparent lack in tolerance and rebound, and by the moderate increase in cardiac output associated with the treatment.