A brief overview of mechanistic studies on the reactions of different Pt( ii ) complexes with nitrogen- and sulfur-donor biomolecules is presented. The first part describes the results obtained for substitution reactions of mono-functional Pt( ii ) complexes with different biomolecules, under various experimental conditions (temperature, pH and ionic strength). In addition, an overview of the results obtained for the substitution reactions of bi-functional Pt( ii ) complexes, analogous to cisplatin, with biomolecules is given. The last part of this report deals with different polynuclear Pt( ii ) complexes and their substitution behaviour with different biomolecules. The purpose of this perspective is to improve the understanding of the mechanism of action of Pt( ii ) complexes as potential anti-tumour drugs in the human body. The mechanistic behaviour of different mono- and bifunctional as well as mono- and dinuclear Pt( ii ) complexes is reviewed in reference to their substitution reactions with biologically relevant nucleophiles.