We investigated the hypothesis that at least part of the vasopressor activity of noradrenaline (NA) and angiotensin II (Ang II) in humans is due to the activation of receptor-dependent calcium channels. Thirty patients (15 aged 50-65 years and 15 aged 66-80 years) with diastolic blood pressure of 95-120 mm Hg were given placebo (P) for 4 weeks, and then nitrendipine (N) 20-40 mg/day for 12 weeks. After 4 weeks on placebo, and again after 12 weeks on nitrendipine, NA 40, 80, 160, and 320 ng/kg/min, followed by Ang II 2.5, 5, and 10 ng/kg/min, was infused intravenously, and steady state systolic, diastolic, and mean arterial blood pressure and heart rate were measured. Older patients were found to be significantly less sensitive than younger patients to the pressor effects of NA. N decreased NA sensitivity, more in younger than older patients. Older patients were significantly more sensitive than younger patients to the pressor effect of Ang II. N also decreased Ang II sensitivity, more in older than younger patients. We conclude that at least some of the vasopressor activity of NA and Ang II is due to activation of calcium channels, and that these effects are age dependent.