Nitrendipine, a new calcium-channel antagonist, was used to treat 25 children (aged 6 months to 17 years) with severe hypertension. Systolic and diastolic blood pressures (mean±SEM) fell from 148±2/99±2 mm Hg to 128±4/77±3 mm Hg after 24 hours and to 121±2/75±2 mm Hg after 2 weeks. No further reductions in systolic or diastolic blood pressure were observed after continued therapy. Transient reflex tachycardia occurred during the first week of therapy. Other adverse effects were uncommon and included headaches, flushing, palpitations, and edema. Pharmacokinetic parameters were estimated at steady state after an oral dose of 0.56±0.04 mg/kg in 13 children. Although absolute oral bloavailability could not be determined, estimates of the area under the plasma concentration versus time curve, the apparent peak serum concentration, and the apparent time at which the peak serum concentration occurred indicated that both the rate of absorption and oral bloavailability are variable. Coadministration of nitrendipine with food decreased the rate of absorption and may have reduced oral bloavailability. A relationship between age and the apparent plasma elimination half-life of nitrendipine was not observed. Nitrendipine, 0.25 to 0.5 mg/kg per dose administered orally every 6 to 12 hours, appeared to be an effective and safe treatment for resistant hypertension in infants and children.