The organ distributions of 4 different 99mTc-dimercaptosuccinate complexes (Tc-DMS, complexes 1-4) were determined using mice and were evaluated as renal imaging agents. The highest kidney uptake was observed with complex 2: 21.7% of dose, 3 h after injection. The biologic distributions and gel chromatographic analyses using carrier 99Tc and 113Sn indicated that there was little possibility of mixed metal complexes of the type Tc-Sn-DMS; rather they contained only Tc + DMS. The labeling procedure for 99mTc-DMS as a renal agent proceeded in 2 steps: a rapid formation of complex 1 and a slower, rate-determining step from complex 1 to complex 2. A reproducible lyophilized kit was prepared. The yield of complex 2 greatly depended on the reconstitution volume of 99mTcO4-; the yield averaged 89% using 2 ml of 99mTcO4- eluate.