The purpose of this study was to evaluate if there is an association between the antithyroid drug dose that is needed to establish euthyroidism and thyroid blood flow measurements. A total of 23 Graves' disease patients with euthyroidism taking antithyroid drug therapy were enlisted to undergo spectral duplex sonography of the thyroid arteries and color-flow mapping of the thyroid gland. Color pixel density (CPD) was calculated with computer assistance from the color-flow maps. There was a strong correlation between the CPD and methimazole dose (rp = 0.79). Methimazole maintenance dosage could be predicted from CPD values with a coefficient of determination of 0.62. In conclusion, CPD measurements could be a useful tool for the clinical endocrinologist to estimate the antithyroid drug dose that is needed to maintain euthyroidism.