Several avian and mammalian c-type lysozymes were chromatographed on chelated (to iminodiacetate) and immobilized transition metal ions (Co2+, Ni2+, Cu2+ and Zn2+) under a variety of experimental conditions. The varied affinity of evolutionary variants of the lysozyme family for chelated metal ions, IDA-M(II), can be rationalized primarily in terms of the presence, multiplicity and microenvironments of histidine residues. The chromatographic resolution of some of these closely related proteins attests to the analytical power of immobilized metal-ion affinity chromatography.