The most commonly used methods for determining thyroxine binding globulin(TBG) concentrationas the total thyroxine-binding capacity utilize electrophoretic seperation of serum. Although technically simple, the electrophoretic method is time consuming and is limited in the number of samples which can be run in a single assay. The author presented a single T4 load ion exchange resin method as an approach to simplify the technique as with clinical practicability and results were analyzed. For construction of the standard curves, serum mixtures were diluted with barbital buffer which effectively blocked T4-binding to TBPA. For each serum dilution, a constant amount of T4-125I and increments of unlabelled T4 were added. After incubation in water bath, resin beads were dispensed to the samples which binded all T4 not bound to TBG. The radioactivity in the supernatant was counted in the gamma scintillation counter. Each standard curve was plotted from the percent counts in the supernatant and total T4 in each tube. Unknown samples were diluted to 1:40 and ran at a single T4 loading concentration, and the TBG capacity of the samples was able to be read on the standard isobars. The following results were obtained. 1) Mean and standard deviation for TBG capacity in normal population was 28.6±5.09 ㎍ T4/100ml. 2) 24.9±3.87 ㎍ T4/100ml in hyperthyroidism showed low TBG capacity tendency comparing to normal population(p<0.025). 3) 31.0±2.40 ㎍ T4/100ml in hypothyroidism showed high TBG capacity tendency comparing to normal population. 4) Reversed correlationship existed between TBG capacity and T3 resin uptake (r=-0.624), TBG capacity and serum T4 value (r=-0.859), and TBG capacity and free thyroxine index (r=-0.623). The author assumes that this method of assay is considerably simpler in instrumentation and technique than any other assays traditionally being used, and seems to be more practical for routine clinical laboratory use.