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<p>Abstract</p> <p>Background</p> <p>Endothelial function in hypercholesterolemic rabbits is usually evaluated <it>ex vivo</it> on isolated aortic rings. <it>In vivo</it> evaluation requires invasive imaging procedures that cannot be repeated serially.</p> <p>Aim</p> <p>We evaluated a non-invasive ultrasound technique to assess early endothelial function in rabbits and compare data with <it>ex vivo</it> measurements.</p> <p>Methods</p> <p>Twenty-four rabbits (fed with a cholesterol diet (0.5%) for 2 to 8 weeks) were given progressive infusions of acetylcholine (0.05–0.5 μg/kg/min) and their endothelial function was assessed <it>in vivo</it> by transcutaneous vascular ultrasound of the abdominal aorta. Ex vivo endothelial function was evaluated on isolated aortic rings and compared to <it>in vivo</it> data.</p> <p>Results</p> <p>Significant endothelial dysfunction was demonstrated in hypercholesterolemic animals as early as 2 weeks after beginning the cholesterol diet (aortic cross-sectional area variation: -2.9% vs. +4% for controls, p < 0.05). Unexpectedly, response to acetylcholine at 8 weeks was more variable. Endothelial function improved in 5 rabbits while 2 rabbits regained a normal endothelial function. These data corroborated well with <it>ex vivo</it> results.</p> <p>Conclusion</p> <p>Endothelial function can be evaluated non-invasively <it>in vivo</it> by transcutaneous vascular ultrasound of the abdominal aorta in the rabbit and results correlate well with <it>ex vivo</it> data.</p>