The reaction of L-selenomethionine (SeMet) with [Pt(dien)Cl]Cl [dien = diethylenetriamine] was studied using ¹H and ¹⁹⁵Pt NMR spectroscopy. The results of this investigation are being used to interpret corresponding studies with other platinum complexes, many of which are structurally similar to the anticancer drug cisplatin. [Pt(dien)Cl]Cl possesses a single leaving group that limits the number of coordination sites on the molecule. This, in turn, significantly limits the number of adducts formed. Additionally, [Pt(dien)Cl]Cl is water soluble, which eliminates the necessity of any preparatory steps (e.g. treatment with AgNO₃). One product, [Pt(dien)(SeMet-Se)]²⁺ is expected; however, two signals that correspond to the methyl group of SeMet are observed. The appearance of two closely spaced signals is most likely due to slow exchange between two chiralities at the Se atom. One ¹⁹⁵Pt NMR resonance was observed; to our knowledge, this is the first reported ¹⁹⁵Pt NMR shift of a molecule containing a Pt-Se bond. When [Pt(dien)Cl]Cl is reacted with a mixture of methionine (Met) and SeMet, reaction with SeMet is kinetically favored. After several days, a mixture of [Pt(dien)(SeMet-Se)]²⁺ and [Pt(dien)(Met-S)]²⁺ is observed, indicating that Met can displace SeMet. Thus, although only a subset of proteins have selenium-containing amino acids, platinum complexes could target them kinetically.