The review is devoted to analysis of published and personal data on the role of the disulphide bridges of residual protein (RP) in the structuro-functional organization of chromosomal DNA. A comparative study is made of the effect of different S-S cleaving agents (2-mercaptoethanol, dithiothreitol, sodium borhydride, glutathione reductase) on natural DNA-RP complexes isolated from different cells of eukaryotes and prokaryotes. It is shown that, depending on the conditions of incubation (concentration of thiol, pH of the medium, duration of treatment), the thiols break down the DNA-RP complex into double-stranded fragment-subunits of different size (5 10 5 , 18-20 10 6 , 70 10 6 D). It was found that in the DNA-RP complexes specific S-S bonds are present (thiol-sensitive in a neutral and/or acid medium, glutathione reductase-sensitive) which may control the different levels of organization of DNA in the chromosome (gene, transcription, replicon, domain). A possible model of the quasisubunit organization of chromosomal DNA with the participation of polypeptide S-S bonds and the complementary sticky ends of the DNA subunits is discussed.