Genetic and physiological variations of the haem-binding proteins were studied in chickens by means of starch gel electrophoresis and other methods. No genetically controlled variability was found. Three electrophoretically different forms of the haem-binding proteins were observed. The permanent haem-binding protein (methaemalbumin) occurred from hatching until late age and was present in the blood serum and in some other organs. The juvenile haem-binding protein (haptoglobin) was present in the serum of hatchlings of both sexes and during sexual maturation it disappeared from the blood and was not renewed due to the physiological changes in the organism. The liver haem-binding protein is a fast migrating protein, having properties different from those of the permanent and the juvenile haem-binding proteins.