Calcium antagonists attenuate the development of aortic lesions in cholesterol-fed rabbits. This study was undertaken to examine the influence of isradipine (dose: 0.3 mg/kg per day orally) on the histological components of these lesions in New Zealand White rabbits (age: 12 weeks, weight: 2-2.5 kg). Five groups of animals were fed standard chow with the following supplements for 3 weeks: Group 1, no supplements; Group 2, 40 g cholesterol; Group 3, 60 g cholesterol; Group 4, 40 g cholesterol + isradipine; Group 5, 60 g cholesterol + isradipine. After 3 weeks, the animals were killed and the aorta prepared for morphometry. The volume of intima/cm aorta was estimated and the volume fraction (Vv) of the intima occupied by components of the lesions was estimated by point counting. By integrating these two measurements the volume/unit length (mm3/cm) of the following components of the aorta were estimated: intima, non-cellular components, endothelial cells, myointimal cells, lipid accumulating myointimal cells and foam cells. Cholesterol feeding for 3 weeks was associated with significant increases in the volume of non-cellular components of the intima, endothelial cells, myointimal cells, lipid accumulating myointimal cells and foam cells. Administration of isradipine significantly reduced all these parameters. It is concluded that isradipine attenuates cellular hyperplasia and accumulation of non-cellular components of lesions in cholesterol fed rabbits.