There is no repont of using of radioactive tin for skeletal imaging. As previously reported, /sup 113/Sn-citrate had very strong affinity for bone. Among the isotopes of tin, /sup 117m/ Sn had ideal physical characteristics for gamma camera systems. In order to evaluate possibilities of bone scanning with / sup 117m/Sn, the present study was performed. Before embarking on the production of /sup 117m/ Sn, we decided to use /sup 113/Sn in a series of experiments with rats. Localization of bone-seeking compounds in the skeleton differs considerably with the age of animals. Consequently, /sup 85/Sr (as chloride) was used with /sup 113/Sn-citrate in these experiments as a biological standard. / sup 113/Sncitrate and /sup 86/Sr-chloride were injected intravenously to each animal, respectively. The animals were sacrificed serially from 1 to 24 hrs after injection. The soft tissue (except kidney) and blood concentrations of / sup 113/Sn-citrate were less than those for /sup 85/Sr at 1 hr and 3 hrs after injection, and were similar to those for /sup 85/Sr at 24 hrs after injection, whereas the skeletal concentration of /sup 113/Sncitrate were slightly less than those for /sup 85/Sr from 1 to 29 hrs after injection. The cumulative urinary excretionmore » of /sup 113/Sn at 3 hrs was approximately 54% (compared with 3% of /sup 85/Sr), the residue, which was almost accumulated in bone, was excreted very slowly in biological half-life of 31.5 days. /sup 113/Sn-citrate had excellent biological property for bone scanning agent, compared with /sup 85/Sr. It is the major advantage that /sup 113/Sn-citrate was excreted in urine and was hardly excreted in the gastrointestinal tract. (auth)« less