Résumé : Methods describing isolation, purification and characterization of two avian myoglobins are reported. Chicken myoglobin was extracted at 55 to 90 p. cent ammonium sulfate saturation, while penguin myoglobin was isolated by low temperature fractionation using ethanol in the presence of metallic ions. Both were purified by gel filtration and chromatography on CM Sephadex and their homogeneity was tested by zone electrophoresis with different gels. The amino acid compositions have been determined. Chicken hemoprotein appears very similar to previously studied myoglobin, but penguin hemoprotein differs significantly, essentially by a higher amount of methionine. Both proteins have glycine as the aminoterminal residue. The molar extinction coefficients and the reduced mean residue optical rotation were found to be identical. © 1972.