In order to develop technetium-99m-labelled human albumin microsphere (HAM) for lung scintigraphy, various experiments such as preparation and fractionation of HAM, establishment of optimal labelling conditions, determination of radiochemical purity, stability test and biodistribution of Tc-99m- HAM were carried out. HAM was prepared from the suspension of I mi aqueous human serum albumin (25%) in 130 ml of olive oil at 130∼135°with vigorous stirring. The resulting HAM was fractionated with microsieve to get the desired particle size (15∼50 μ) and autoclaved for sterilization. The HAM particles were treated with stannous chloride and the pH of the suspension was adjusted to 3.0∼3.5 with phosphate buffer. After freeze-drying the contents of single reaction vial containing 5 mg of HAM and 0.2 mg of SnCl2 it was reacted with Na99mTcO4. The labelling yield was higher than 99.5% and the stability of Tc- 99m-HAM was high enough to maintain 99.1% of radiochemical purity up to 24 hours. Lung and liver uptake in mice was found to be 94% and 0.9%, respectively. Excellent rabbit and human lung scans were also obtained.