The ammine/amine platinum(IV) dicarboxylates have been developed as orally active platinum antitumor agents, and one of these, [PtCl2(NH3)(C6H11NH2) (OCOCH3)2] (JM216), is undergoing clinical trials at present. A synthesis method was developed to radiolabel JM216 with carbon 14 at the carboxylate carbon. The labeling efficiency was 92%, and the purity as shown by high-performance liquid chromathography (HPLC) was 96% after recrystallisation. The radiolabeled JM216 was given orally to BALB/c mice and detailed tissue-distribution data were obtained (blood plasma, kidney, liver, spleen, brain, lung, muscle and skin) for time points of 2 h and 2, 6 and 10 days. Comparison of these data with previously reported data for distribution of platinum obtained by atomic absorption spectroscopy has shown distinct differences, especially for the liver and the kidney. This clearly indicates a difference in behaviour between the labeled ligand and the platinum centre, suggesting detachment of the ligand in vivo.