An attempt is made to establish the historical context in which the structure and function of haemoglobin were investigated by X-ray crystallographers in the 1940s and 50s. It is concluded that until the 1960s the interpretations of the data of crystallographic investigations were dependent upon the results of applying traditional techniques of physical and organic chemistry. In the case of haemoglobin, no less than in those of smaller organic molecules, crystallographic studies in the 1940s and early 50s served to validate, (...) and metricize conclusions already suggested or adopted on other grounds, but the subsequent tracing of the actual conformation of the polypeptide chains in the globin portion of the molecule was a unique achievement of the X-ray crystallographers and marked the beginning of the independent establishment of structures by this profession. The impact of this achievement upon the structure-function relationships of haemoglobin is discussed briefly. (shrink)