The anticancer drug cisplatin is activated via hydrolysis before binding to DNA. Although [Pt(dien)Cl]⁺1 (where dien is diethylenetriamine) has been extensively used as a model for the first step in the binding of cisplatin to DNA and other biological targets, the hydrolysis behaviour of this complex is not well understood. In this work we have used a two-dimensional [¹H,¹⁵N] NMR approach, and have established correlations between δ(¹⁵N) and ¹J(¹⁹⁵Pt–¹⁵N) for Pt–NH₂ and Pt–NH groups which are useful for assignment of resonances and identification of trans ligands, as has been previously recognised for Pt–NH₃ complexes. Although it has previously been suggested that the rate of reaction of complex 1 with guanosine 5′-monophosphate is determined by the rate of hydrolysis, no NMR peaks for an aqua intermediate were detectable, and no hydrolysis of 1 alone was observed after 7 d at 298 K. This raises new questions about the mechanisms of such reactions.