This thesis describes an investigation into the use of amperometric techniques for the detection of enzyme catalysed reactions. Enzymes catalyse a vast number of biological reactions and the detection of their activity can lead to the development of analyses for their substrates.The specificity with which the enzyme recognises its substrate is unique and cannot be easily mimicked by chemical catalysis.Enzymatic analyses can therefore be highly discriminating, they are also often the best methods for biological analyses as they can be carried out under mild conditions. The isolation of enzymes for use in vitro can also enable substrate analogues, which the molecule would not normally encounter, to be detected using that enzyme. Traditional methods of detecting enzyme activity rely on expensive equipment and skilled operation.Current trends in analysis, especially in the medical field, are towards methods which can be used away from laboratories and devices capable of such analyses are called biosensors.Work carried out in this thesis uses the electrochemical technique of amperometry for the detection of enzyme catalysed reactions The simple instrumentation and rapidity associated with this technique facilitates the development of biosensors from the analyses described. The thesis examines three different systems.The first is a specific sensor for paracetamol (acetaminophen), the second a more widely applicable assay for dehydrogenases .This analysis is based on the amperometric detection of NADH using the mediated electrochemistry of the enzyme diaphorase.The same system has also been used to study the kinetics of the overall reaction which are compared with a kinetic analysis carried out by conventional methods. The final assay is for the detection of catalase, this extremely active enzyme is also conjugated to antibody molecules such that an enzyme linked immunosorbent assay (ELISA) with amperometric detection can be developed.