A procedure for the radiochemical purity control of99mTc-(2,3-dimercaptosuccinic acid) (DMSA), used as a renal scintigraphic agent is described. The proposed chromatographic system entails the use of two successive solvents, first MEK and second aqueous solution of 5% glycine, on the same supporting medium Gelman ITLC-SG. The procedure is fast and leads to separation and estimation of free pertechnetate, hydrolyzed form of99mTc and99mTc — DMSA. This system is superior to the others reported in the literature as the spots of the different species are more distinguished and more concentrated. Its reliability has been studied using dimercaptosuccinic acid kits of different manufacturers and the results have been checked biologically.