The intimate structure of the complexes located at the sites of DNA loops attachment to the nuclear skeleton was analysed. It is shown that: there are at least three components of the attachment site complex: DNA, protein, RNA; protein moiety consists of 7-8 species with Mr 70-17 kDa. Their association with DNA is resistant to ionic detergents, high salt and urea treatments. The DNA-protein complex is also resistant to the SDS-pronase-phenol deproteinisation procedure; the buoyant density of the complex is the same as DNA density. RNase digestion at low ionic strength reduces density of the complex while the same treatment at 0,4 M NaCl has no effect; DNA-protein complexes isolated with urea-high salt treatment are visualised as globular particles 25-35 nm in diameter with DNA loops attached. These particles were not observed after detergent treatment although protein composition of the complex remained the same.