Patrick Maxwell is Professor of Nephrology at Imperial College. He has received several major awards, including the Goulstonian Lecturership of the Royal College of Physicians in 2001. He has made an outstanding contribution to understanding how cells respond to changes in oxygen. His work is of fundamental importance in unravelling the nature of many human diseases, including disorders of the kidney, cardiovascular disease and cancer. As a nephrologist, it was natural that the starting point for this work was the role of the kidney in regulating red blood cell production through the synthesis of erythropoietin. His first major contribution in this area was to identify the interstitial fibroblast as the cell responsible for producing erythropoietin. Professor Maxwell demonstrated that the underlying hypoxic response system operated in all mammalian cell types, implying that it had other functions besides controlling erythropoietin production. This has been extensively confirmed; indeed it is now recognised that the underlying Hypoxia inducible factor (or HIF-1) system is a master regulator controlling a very wide range of processes, including angiogenesis and cellular metabolism. He has made definitive observations concerning how the system operates, and what it does. His discoveries include demonstrating that the von Hippel Landau (VHL) tumour suppressor protein is required for HIF regulation, identifying prolyl hydroxylation as the oxygen sensitive modification which regulates the HIF:VHL interaction and showing that HIF prolyl hydroxylase act as oxygen sensors. He has shed light on one of the most basic processes in biology and one that is essential for health and disease.