John Kilmartin is a pioneer in the molecular analysis of the spindle pole, the unique cellular structure that organises the mitotic spindle during cell division. Using budding yeast as a model system, he has combined biochemical purification, immunoelectron microscopy and genetic studies to analyse the organisation and function of this structure. He and others have defined the major components in a systematic manner, demonstrated the structural principles which underlie the complex layered features, and identified components which link the pole bodies to the spindle microtubules. His analysis has elucidated the way in which precise duplication of the spindle pole is achieved during each cell cycle. John also performed elegant studies on the structure and function of haemoglobin. Using chemical and enzymatic modification of specific residues, he was the first to identify amino acids responsible for the Bohr effect, the important physiological mechanism by which pH changes regulate the affinity of haemoglobin for oxygen.