OBJECTIVE To find the appropriate contrast agent dose for gadolinium-enhanced magnetic resonance (MR) angiography by using individual measurement of contrast agent transit times in a randomized study. METHODS A total of 34 patients with disease of the aorta or its major branches or both were randomly assigned to receive a dose of 0.1, 0.2, or 0.3 mmol of gadopentetate dimeglumine per kilogram of body weight. Initially, contrast agent transit times were measured with use of a turbo fast-low-angle-shot sequence. Subsequently, a three-dimensional fast imaging with steady-state precession sequence (7.3-msec repetition time, 2.8-msec echo time) was used for breath-hold MR angiography. Gadopentetate dimeglumine was injected with an MR-compatible power injector. Efficacy was evaluated by measurement of vessel enhancement and by clinical correlation of MR angiograms with x-ray angiograms. RESULTS Evaluation of contrast agent transit time was possible in all patients with the test doses, which provided contrast-enhanced MR angiograms of constant quality. Neither vessel enhancement nor diagnostic information was significantly different across the these study groups. CONCLUSIONS The clinical gadolinium dose of 0.1 mmol/kg is sufficient for diagnostic assessment of the aorta and its major branches at contrast-enhanced MR angiography. High-dose studies appear not to be required for these large vessels.