Professor John Miners has made sustained contributions to the characterisation of the enzymatic basis of drug metabolism, which underpins the individualisation of drug therapy in humans. His research has: identified sources of variability in drug metabolism, especially drug-drug interactions and pharmacogenetics; characterised the substrate and inhibitor selectivities and structure-function relationships of the key drug metabolising enzymes cytochrome P450 and UDP-glucuronosyltransferase; and developed in vitro experimental paradigms that predict drug metabolism and disposition parameters in humans. The research has played a pivotal role in establishing drug metabolism as a predictive science that supports preclinical drug development and the clinical use of drugs.