The work described in this thesis falls into two areas of clinically significant binding the interaction of sodium nitroprusside with biological macromolecules, and the consequence of bilirubin to albumin binding in the assay for bilirubin. In Part 1; Chapter 1 is a general introduction reviewing the chemistry of sodium nitroprusside and its medical application. Chapter 2 is concerned with the evaluation of aquocobalamin as a cyanide trapping agent and the stability of sodium nitroprusside. Chapter describes 13C NMR and EHMO studies of the binding of cyanoferrates to cobalarains and cobaloximes. Chapter 4 reports on the pharmacological consequences of the interaction of nitroprusside with aquocobalamin. The second section of this chapter considers the interaction of nitroprusside with albumin and haemoglobins. In Part 2 of this thesis Chapter 5 reviews the methods used in bilirubin assay. Chapter 6 describes fluorescence and solid state studies investigating the binding of bilirubin to albumin and evaluates the ability of various "accelerators" to interfere with the binding of bilirubin to albumin in the diazo method of bilirubin assay. Chapter 7 considers the problems involved in using diazonium salts in the wet chemistry assays of bilirubin and describes an initial study evaluating the use of heterocyclic diazo compounds in the diazo dry base multi-layer film method of bilirubin assay.