Complete oxygen dissociation curves for red cell suspensions of three haemoglobinopathies, namely haemoglobin (Hb) H, Hb Köln and Hb Tak/beta thalassaemia diseases, were measured using automatic recording methods. These curves were left-shifted compared with the normal red cell curve and showed a biphasic shape as a result of co-existence of the high and normal affinity haemoglobin components. Computer-assisted simulation of these biphasic curves enabled us to infer the curves for the pure abnormal haemoglobins and their fraction in the total haemoglobin of the red cell. The inferred values of fraction agreed with those determined by haemoglobin type analysis or the literature values. The curve for Hb Köln red cells deviated from the normal red cell curve in the whole range of oxygen saturation, whereas the curve for Hb H was close to the normal curve at the middle and upper portions. This difference in deviation was ascribed to a possible interaction between Hb Köln and Hb A through subunit exchange, and its absence between Hb H and Hb A. The present results indicate that measurement of the complete oxygen dissociation curve is important for the detection of non-interacting variants such as Hb H and is useful for inferring the functional properties of haemoglobin components that are not easily isolated.