Utilizing the commercial radioimmunoassay kit, the author assayed HGH and evaluated the problems of the method. The method had the sensitivity of 0.5 mug/ml degree and could determine the plasma HGH concentration directly without the help of plasma extraction. Also it was specific for the HGH, when tested by a dilution method using test utilizing the plasma of the acromegalic patient. The author also obtained the $^{125}I$ labelled HGH of specific activity of $156.3{mu}Ci/{mu}g$, performing the chloramine-T method.