Abstract: 110mAg labeling of metallothionein (MT) and MT-IgG in the state of Ag(NH3)2+ are carried out in 0.050mol/1 barbitone buffer with pH 8.0. All labeling yields attained approximately 100%. And specific radioactivity is as high as 12.21×106Bq/mg MT and 4.07×106Bq/mgMT-IgG, when 4.63×107 Bq/mg irradiated Ag (110mAg) is used in the experiment.Biodistribution differences of 110mAg(NH3 )2+, 110mAg-MT and 110mAg-MT-IgG in Swiss mice within 6 hours post tail i.v. injection are distinct. 110mAg(NH3)2+ and 110mAg-MT-IgG are mainly removed by liver, while 110mAg-MT accumulates in kidneys rapidly and highly. 110mAg(NH3)2+ and 110mAg-MT-IgG reach their highest uptake in liver, 69% ID/g in 30min and 65% ID/g in 45min. But 110mAg(NH3)2+ is removed much faster than 110mAg-MT-IgG.Their retention in 6 hours is 20% ID/g and 50% ID/g respectively. 110mAg-MT does not accumulate much in liver, the maximum is 30% ID/g, and its decrease is relatively slow. On the other hand, 110mAg-MT accumulates highly in kidneys, up to 210% ID/g in 20min, and maintains above 130% ID/g for one hour. In contrast, the concentrations of 110mAg(NH3)2+ and 110mAg-MT-IgG in kidneys are low, only 10%ID/g and 6%ID/g at the highest levels. With regard to the blood clearance of the three radiolabeled compounds, 110mAg-MT is the fastest, and 110mAg(NH3)2+ maintains relatively high level in blood. The different pharmacokinetics of 110mAg(NH3)2+, 110mAg-MT and 110mAg-MT-IgG, indicates that 110mAg radiolabeling of MT and its conjugated IgG are stable in vivo. This preliminary study on the labeling of IgG with 110mAg would be of value in developing MT as a bifunctional chelating agent for 111Ag in radioimmunotherapy.