A study was undertaken in order to find a single quickly obtained value of radioiodine uptake which might be as useful as an entire uptake curve for the clinical classification of thyroid patients. As such the "%/hr." value was selected[long dash]the per cent of the total dose of I131 collected by the thyroid during the 1st few hours after its admn. (2-6 hrs.) divided by the time between admn. and observation. Although this value was dependent upon the time of measurement, it was found to be as useful as detn. of basal metabolic rate, protein-bound I or maximum uptake of I131 in the thyroid.