Interaction of ATP with cisplatin in the pH range 1.9-9.5 was studied by NMR. A new complex with the composition Pt(NH 3 ) 2 (ATP) 2 , which formed very slowly after cisplatin was added to ATP solution, was identified by DOSY and long range 1 H 1 5 N HMQC experiments. In the complex, ATP bound Pt at N7, and the N7 Pt bond showed the nature of kinetically inert interaction. At low pH, beside the 2:1 complex of N7 type, a 1:1 complex of N1 type co-existed in the solution but the binding interaction was ionic and the complex exchanged rapidly with free ATP on the NMR time scale.