It is our purpose to review recent experiments on haemoglobin in order to discuss them in terms of the two state model of cooperativity. Excellent previous reviews are available of the chemistry of haemoglobin (Antonini & Brunori, 1971; Gibson, 1959b) which are referred to when possible. The plethora of data necessitates that a selection must be made in a review. An intentionally wide range of experiments is selected to exhibit

To the Chemist, it has long been second nature to work with separate, purified substances. Biochemists and molecular biologists have now largely achieved the same working position, with their powerful separation techniques of ultracentrifugation, electrophoresis, chromatography and the like. For the cell biologists, it is a much more recent phenomenon that widespread attention is being directed towards quantitative measurement of properties in isolated, homogeneous cell types. The richness and diversity of cell systems beg for cleverness on the part of the experimenter.