Preparations of horse heart cytochrome c have been obtained immobilized on Sepharose derivatives via lysine epsilon-amino groups, carboxyl groups of aspartic and glutamic acid residues, methionine and histidine residues as well as imidazole groups additionally introduced by means of chemical modification of free carboxyl groups by histamine. Dissociation constants have been determined for complexes of adrenodoxin, hepatoredoxin, cytochrome b5 heme-containing fragment and myoglobin with preparations of cytochrome c immobilized via lysine residues (adsorbent I) or additionally introduced imidazole groups (adsorbent II). The latter is found to possess a 2-3 times greater affinity for adrenodoxin and hepatoredoxin than the former. The affinity of the proteins studied for the adsorbent II constitutes the following sequence: adrenodoxin greater than or equal to hepatoredoxin greater than cytochrome b5 heme-containing fragment greater than myoglobin. The adsorbent II is shown to be effective when used for purification of hepatoredoxin, adrenodoxin, cytochrome b5 and isolation of cytochrome b5 heme-containing fragment.